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 A218755 #21 May 13 2013 01:54:23 %S A218755 6,42,330,510,690,798,870,1410,1518,1590,1770,1806,2490,3102,3210, %T A218755 3318,3894,4110,4326,4470,4686,5010,5190,5370,5478,6486,6810,7062, %U A218755 7890,8070,8142,8646,8790,9366,9510,10410,10770,11022 %N A218755 Denominators of Bernoulli numbers which are == 6 (mod 9). %C A218755 The sequence contains the elements of A090801 which are == 6 (mod 9). %C A218755 Conjecture: all first differences 36, 288, 180, 180,... of the sequence are multiples of 36. %C A218755 The conjecture is true, since elements of A090801 are 2 mod 4. - _Charles R Greathouse IV_, Nov 22 2012 %H A218755 Charles R Greathouse IV, <a href="/A218755/b218755.txt">Table of n, a(n) for n = 1..10000</a> %t A218755 Take[Union[Select[Denominator[BernoulliB[Range[1000]]],Mod[#,9]==6&]],60] (* _Harvey P. Dale_, Nov 28 2012 *) %o A218755 (PARI) is(n)=if(n%36-6, 0, my(f=factor(n)); if(vecmax(f[, 2])>1, return(0)); fordiv(lcm(apply(k->k-1, f[, 1])), k, if(isprime(k+1) && n%(k+1), return(0))); 1) \\ _Charles R Greathouse IV_, Nov 26 2012 %Y A218755 Second subset of the Bernoulli denominators: A090801 which are == 3 (mod 9). %K A218755 nonn,easy %O A218755 1,1 %A A218755 _Paul Curtz_, Nov 05 2012