OFFSET
1,1
COMMENTS
1806 = 2 * 3 * 7 * 43.
All terms are multiple of a(1) = 42.
For these numbers numerator(B_{n}) mod denominator(B_{n}) = 1.
In 2005, B. C. Kellner proved E. W. Weisstein's conjecture that denom(B_n) = n only if n = 1806.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1000
EXAMPLE
Bernoulli B_{42} is 1520097643918070802691/1806, hence 42 is in the sequence.
MAPLE
with(numtheory): P:=proc(q, h) local n; for n from 2 by 2 to q do
if denom(bernoulli(n))=h then print(n); fi; od; end: P(10^6, 1806);
MATHEMATICA
Select[Range[0, 1000], Denominator[BernoulliB[#]] == 1806 &] (* Robert Price, Apr 21 2016 *)
Select[Range[42, 30000, 42], Denominator[BernoulliB[#]]==1806&] (* Harvey P. Dale, Jun 01 2019 *)
PROG
(PARI) lista(nn) = for(n=1, nn, if(denominator(bernfrac(n)) == 1806, print1(n, ", "))); \\ Altug Alkan, Apr 22 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Apr 21 2016
EXTENSIONS
More terms from Altug Alkan, Apr 22 2016
STATUS
approved