# Bernoulli numbers modulo p#

AUTHOR:

• David Harvey (2006-07-26): initial version

• William Stein (2006-07-28): some touch up.

• David Harvey (2006-08-06): new, faster algorithm, also using faster NTL interface

• David Harvey (2007-08-31): algorithm for a single Bernoulli number mod p

• David Harvey (2008-06): added interface to bernmm, removed old code

sage.rings.bernoulli_mod_p.bernoulli_mod_p(p)#

Return the Bernoulli numbers $$B_0, B_2, ... B_{p-3}$$ modulo $$p$$.

INPUT:

p – integer, a prime

OUTPUT:

list – Bernoulli numbers modulo $$p$$ as a list of integers [B(0), B(2), … B(p-3)].

ALGORITHM:

Described in accompanying latex file.

PERFORMANCE:

Should be complexity $$O(p \log p)$$.

EXAMPLES:

Check the results against PARI’s C-library implementation (that computes exact rationals) for $$p = 37$$:

sage: bernoulli_mod_p(37)
[1, 31, 16, 15, 16, 4, 17, 32, 22, 31, 15, 15, 17, 12, 29, 2, 0, 2]
sage: [bernoulli(n) % 37 for n in range(0, 36, 2)]
[1, 31, 16, 15, 16, 4, 17, 32, 22, 31, 15, 15, 17, 12, 29, 2, 0, 2]


Boundary case:

sage: bernoulli_mod_p(3)



AUTHOR:

– David Harvey (2006-08-06)

sage.rings.bernoulli_mod_p.bernoulli_mod_p_single(p, k)#

Return the Bernoulli number $$B_k$$ mod $$p$$.

If $$B_k$$ is not $$p$$-integral, an ArithmeticError is raised.

INPUT:

• p – integer, a prime

• k – non-negative integer

OUTPUT:

The $$k$$-th Bernoulli number mod $$p$$.

EXAMPLES:

sage: bernoulli_mod_p_single(1009, 48)
628
sage: bernoulli(48) % 1009
628

sage: bernoulli_mod_p_single(1, 5)
Traceback (most recent call last):
...
ValueError: p (=1) must be a prime >= 3

sage: bernoulli_mod_p_single(100, 4)
Traceback (most recent call last):
...
ValueError: p (=100) must be a prime

sage: bernoulli_mod_p_single(19, 5)
0

sage: bernoulli_mod_p_single(19, 18)
Traceback (most recent call last):
...
ArithmeticError: B_k is not integral at p

sage: bernoulli_mod_p_single(19, -4)
Traceback (most recent call last):
...
ValueError: k must be non-negative


Check results against bernoulli_mod_p:

sage: bernoulli_mod_p(37)
[1, 31, 16, 15, 16, 4, 17, 32, 22, 31, 15, 15, 17, 12, 29, 2, 0, 2]
sage: [bernoulli_mod_p_single(37, n) % 37 for n in range(0, 36, 2)]
[1, 31, 16, 15, 16, 4, 17, 32, 22, 31, 15, 15, 17, 12, 29, 2, 0, 2]

sage: bernoulli_mod_p(31)
[1, 26, 1, 17, 1, 9, 11, 27, 14, 23, 13, 22, 14, 8, 14]
sage: [bernoulli_mod_p_single(31, n) % 31 for n in range(0, 30, 2)]
[1, 26, 1, 17, 1, 9, 11, 27, 14, 23, 13, 22, 14, 8, 14]

sage: bernoulli_mod_p(3)

sage: [bernoulli_mod_p_single(3, n) % 3 for n in range(0, 2, 2)]


sage: bernoulli_mod_p(5)
[1, 1]
sage: [bernoulli_mod_p_single(5, n) % 5 for n in range(0, 4, 2)]
[1, 1]

sage: bernoulli_mod_p(7)
[1, 6, 3]
sage: [bernoulli_mod_p_single(7, n) % 7 for n in range(0, 6, 2)]
[1, 6, 3]


AUTHOR:

– David Harvey (2007-08-31) – David Harvey (2008-06): rewrote to use bernmm library

sage.rings.bernoulli_mod_p.verify_bernoulli_mod_p(data)#

Compute checksum for Bernoulli numbers.

It checks the identity

$\sum_{n=0}^{(p-3)/2} 2^{2n} (2n+1) B_{2n} \equiv -2 \pmod p$

(see “Irregular Primes to One Million”, Buhler et al)

INPUT:

data – list, same format as output of bernoulli_mod_p function

OUTPUT:

bool – True if checksum passed

EXAMPLES:

sage: from sage.rings.bernoulli_mod_p import verify_bernoulli_mod_p
sage: verify_bernoulli_mod_p(bernoulli_mod_p(next_prime(3)))
True
sage: verify_bernoulli_mod_p(bernoulli_mod_p(next_prime(1000)))
True
sage: verify_bernoulli_mod_p([1, 2, 4, 5, 4])
True
sage: verify_bernoulli_mod_p([1, 2, 3, 4, 5])
False


This one should test that long longs are working:

sage: verify_bernoulli_mod_p(bernoulli_mod_p(next_prime(20000)))
True


AUTHOR: David Harvey