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 A219547 #6 Nov 27 2012 12:04:36 %S A219547 8,16,32,40,48,56,64,80,88,96,104,112,128,136,152,160,176,184,192,200, %T A219547 208,224,232,240,248,256,272,280,296,304,320,328,336,344,352,368,376, %U A219547 384,392,400,416,424,440,448,464,472,480,488,496 %N A219547 Numbers k such that 2 times the least prime factor of 2^k + 1 is not the least m > 1 that divides sigma_k(m). %C A219547 Numbers k with 2*A002586(k) unequal to A066135(k). %C A219547 A066135(n) <= 2*A002586(n) for all n (see Comments in A066135). Sequence gives those k for which A066135(k) < 2*A002586(k). %C A219547 The corresponding least prime factors of 2^k + 1 are A219548. %C A219547 See A007691 for references, links, and additional comments. %F A219547 A066135(a(n)) < 2*A002586(a(n)). %F A219547 A002586(a(n)) = A219548(n). %e A219547 A066135(n) = 6,10,6,34,6,10,6 = 2*A002586(n) for n = 1,2,3,4,5,6,7, and A066135(8) = 84 < 2*257 = 2*A002586(8), so a(1) = 8. %Y A219547 Cf. A002586, A007691, A066135, A219548. %K A219547 nonn %O A219547 1,1 %A A219547 _Jonathan Sondow_, Nov 24 2012