OFFSET
1,1
COMMENTS
Also a(n) are the numbers n such that 1 + Sum[ k, {k,1,n} ] = 1 + n(n+1)/2 divides Product[ k, {k,1,n} ] = n!. A118680[ a(n) ] = 1, where A118680(n) = {2, 2, 7, 11, 2, 11, 29, 37, 23, 1, 67, 79, 23, 53, 11, 137, 1, ...} = Absolute value of numerator of determinant of n X n matrix with M(i,j) = (i+1)/i if i=j otherwise 1. A118680(n) = Numerator[ (1 + n(n+1)/2) / n! ].
MATHEMATICA
Select[Range[1000], Numerator[(1 + #(#+1)/2)/#! ]==1&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Feb 03 2007
STATUS
approved