Tables of Primes  
   Primes to 19 million; twin primes to 394 million; quadruple primes to 500 million.
   http://mathematical.com/primetables.html

Number Fields with Prescribed Ramification  
   Number fields of degree up to seven ramified at only a few small primes.
   http://math.la.asu.edu/~jj/numberfields/

Fermat Quotients Divisible by p  
   Wilfrid Keller and Jörg Richstein. A complete list of solutions (a, p) for odd prime bases a < 1000 and primes p < 10^11: for the single base a = 5 the larger interval p < 2^38.
   http://www.informatik.uni-giessen.de/staff/richstein/cnth/FermatQuotient.html

Curves of Genus 2  
   FTP site maintained by Victor Flynn. Formulae for Jacobian arithmetic and Maple algorithms.
   ftp://ftp.liv.ac.uk/pub/genus2/

Number Field Tables  
   FTP site at the University of Bordeaux. Fields of degree up to 7.
   ftp://megrez.math.u-bordeaux.fr/pub/numberfields

The First 28,915 Odd Primes  
   Tabulated using a simple C program.
   http://www.newdream.net/~sage/old/numbers/primeodd.htm

Extended Counts of Twin Primes  
   By Thomas Nicely. Counts in decades up to 10^12 then in steps of 10^12 up to 3.10^15, giving 3,310,517,800,844 pairs.
   http://www.trnicely.net/twins/tabpi2.html

Multiply Perfect Numbers  
   Over 2000 multiperfect numbers sorted by numerical value and by factorisation.
   ftp://ftp.cs.arizona.edu/xkernel/rcs/mpfn.html

The First 100,000 Prime Numbers  
   A Project Gutenberg etext.
   http://digital.library.upenn.edu/webbin/gutbook/lookup?num=65

The First 498 Bernoulli Numbers  
   A Project Gutenberg etext.
   http://digital.library.upenn.edu/webbin/gutbook/lookup?num=2586

The Value of Zeta(3) to 1,000,000 Decimal Digits  
   A Project Gutenberg etext.
   http://digital.library.upenn.edu/webbin/gutbook/lookup?num=2583

Bernoulli Computations  
   Irregular primes and relative class numbers. Irregular pairs (and Vandiver and cyclotomic residues) for primes up to 8 million. Compiled by Amin Shokrollahi.
   http://www.shokrollahi.com/amin/TAB.html

Factorization Tables  
   Tables of the factorization of sigma(n).
   http://www-staff.maths.uts.edu.au/~rons/fact/fact.htm

Enumeration of Twin Primes and Brun's Constant  
   Enumeration of the twin primes, and the sum of their reciprocals, to 1.6 × 10^15. An improved estimate is obtained for Brun's constant, B2 = 1.90216 05824 ± 0.00000 00030. Error analysis is presented to support the opinion that the stated error bound re
   http://www.trnicely.net/twins/twins2.html

Vanishing Fermat Quotients  
   R. Ernvall and T. Metsänkylä. Tables of the pairs (p,k) such that the Fermat quotient q(k) = (k^{p-1}-1)/p vanishes mod p. The tables cover the primes p up to one million and, for each prime, the range 1 < k < p.
   http://users.utu.fi/taumets/fermat/fermat.htm

Database for Polynomials over the Rationals  
   By Jürgen Klüners and Gunter Malle. Polynomials for all transitive groups up to degree 15, for most of the possible combinations of signature and Galois group. Up to degree 7 the fields with minimal (absolute) discriminant with given Galois group and s
   http://www.iwr.uni-heidelberg.de/groups/compalg/minimum/minimum.html

Dedekind Zeta Functions  
   Tabulated by Eyal Goren using Pari.
   http://www.math.mcgill.ca/goren/ZetaValues/zeta.html

Fermat Near-misses  
   Noam Elkies. Approximate solutions of x^n + y^n = z^n in integers with 0 < x <= y < z < 2^23 and n in [4,20].
   http://www.math.harvard.edu/~elkies/ferm.html

Algorithmic Number Theory: Tables and Links  
   Compiled by Noam Elkies.
   http://www.math.harvard.edu/~elkies/compnt.html

Zeroes of the Riemann Zeta Function  
   By Andrew Odlyzko. The first 100,000 to 8 places, the first 1000 to 1000 places.
   http://www.dtc.umn.edu/~odlyzko/zeta_tables/

Carmichael and Perrin  
   The 150 Carmichael numbers out of 246683 up to 10^16 that are Perrin pseudoprimes.
   http://www.ai.univie.ac.at/carmichael.html

Imaginary Quadratic Fields  
   Tables of the fields with class number at most 23.
   http://www.numbertheory.org/classnos/

Practical Numbers  
   A number is practical if all smaller numbers are sums of distinct divisors. Tables compiled by Guiseppe Melfi.
   http://www.unine.ch/statistics/melfi/pratica.html

Cubic Field Extensions  
   Tables and results on cubic number fields by Daniel A. Mayer.
   http://www.algebra.at/CubicNumberFields.htm

Carmichael Numbers and Lehmer's Problem  
   Carmichael numbers n up to 10^9 together with phi(n), (n-1)/phi(n) and the factorization of n. Compiled by Jan Kristian Haugland.
   http://home.no.net/zamunda/carmichael.txt

Tables and Computations  
   Browsable interfaces to tables and computations on elliptic curves, quadratic forms, and modular forms.
   http://www.math.utexas.edu/users/tornaria/cnt/

Tables of Number Fields  
   Hilbert class field of totally real fields of degree 2, 3 and 4; Totally real fields with small root discriminant; Totally real quintic dihedral fields. By Xavier-François Roblot.
   http://igd.univ-lyon1.fr/~roblot/tables.html

Genus-2 Curves with Small Odd Discriminant  
   FTP site by Michael Stoll, with MAGMA code.
   http://www.faculty.iu-bremen.de/stoll/data/

Database of Local Fields  
   By John W. Jones and David P. Roberts. Tables of low degree extensions of Qp, for small p.
   http://math.asu.edu/~jj/localfields/

Algorithms for Solving Index Form Equations and Computing Power Integral Bases  
   Lists of results, description of algorithms and tables of numerical data, by István Gaál.
   http://www.math.klte.hu/~igaal/algorithm.htm

The Positive Integers  
   Information about the positive integers, with counts of some number-theoretic functions, maintained by Saqib Kadri.
   http://www.positiveintegers.org/

Pseudoprimes and Carmichael Numbers  
   Tables of the Fermat pseudoprimes base 2 up to 10^13 and Carmichael numbers up to 10^17 compiled by Richard Pinch.
   http://www.chalcedon.demon.co.uk/rgep/carpsp.html