OFFSET
1,1
COMMENTS
A045979(n), Bernoulli numbers with denominators 6, are included in the sequence.
Also numbers n such that both n+1 and 2n+1 are not prime. - Alexander Adamchuk, Oct 05 2006
LINKS
Alexander Adamchuk, Oct 05 2006, Table of n, a(n) for n = 1..565
FORMULA
Also numbers n>1 such that A000330[n] = Sum[k^2,{k,1,n}] = n(n+1)(2n+1)/6 divides A001044[n] = Product[k^2,{k,1,n}] = (n!)^2. Also numbers n>1 such that Numerator[n(n+1)(2n+1)/6 /(n!)^2] = 1. - Alexander Adamchuk, Oct 05 2006
MATHEMATICA
Select[Range[2, 1000], Numerator[ #(#+1)(2#+1)/6/#!^2]==1&] (* Alexander Adamchuk, Oct 05 2006 *)
Select[Range[1000], !PrimeQ[ #+1]&&!PrimeQ[2#+1]&] (* Alexander Adamchuk, Oct 05 2006 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 03 2002
STATUS
approved