This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A089644 #20 May 17 2021 04:09:52 %S A089644 7,14,28,35,49,56,70,77,91,98,112,119,133,140,154,161,175,182,196,203, %T A089644 217,224,238,245,259,266,280,287,301,308,322,329,343,350,364,371,385, %U A089644 392,406,413,427,434,448,455,469,476,490,497,511,518,532,539,553,560 %N A089644 Numbers k such that 7 divides the numerator of B(2*k) where B(k) = the k-th Bernoulli number. %H A089644 Amiram Eldar, <a href="/A089644/b089644.txt">Table of n, a(n) for n = 1..10000</a> %F A089644 a(n) = 7*A001651(n). %F A089644 a(n) = 21*(n-1)-a(n-1), with n>1, a(1)=7. - _Vincenzo Librandi_, Nov 16 2010 %t A089644 Select[Range[500], Divisible[Numerator @ BernoulliB[2*#], 7] &] (* _Amiram Eldar_, May 17 2021 *) %o A089644 (PARI) isok(n) = ! ((numerator(bernfrac(2*n))) % 7); \\ _Michel Marcus_, Dec 06 2013 %Y A089644 Cf. A001651, A027641, A027642, A073216. %K A089644 nonn,easy %O A089644 1,1 %A A089644 _Benoit Cloitre_, Jan 01 2004