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 A240767 #29 May 17 2014 02:57:26 %S A240767 2,3,4,7,8,11,12,16 %N A240767 Numbers n such that n^k + (n-1)^k + ... + 3^k + 2^k is prime for some natural number k. %C A240767 a(9) > 19. See A240766 for more information. %C A240767 a(n) is also the n-values such that A240766(n) is nonzero. %C A240767 It is known that a(n) must be == 3 mod 4 or 0 mod 4 (except a(1) = 2) due to the parity of the sum. If an n-value is congruent to 1 mod 4 or 2 mod 4, the sum will always be even and thus, not prime. %C A240767 It is known that 31, 36, 40, 43, 47, 56, 67, 83, and 171 are members of this sequence. %C A240767 If n-1 is not squarefree, then n is not a member of this sequence. %e A240767 2^k is prime for at least one k (and only one k in this instance; k = 1). Thus, 2 is a member of this sequence. %e A240767 3^k+2^k is prime for at least one k (see A082101). Thus, 3 is a member of this sequence. %o A240767 (PARI) a(n)=for(k=1,4000,if(ispseudoprime(sum(i=2,n,i^k)),return(k))) %o A240767 n=1; while(n<200,if(a(n),print(a(n)));n+=1) %Y A240767 Cf. A081507, A082101, A240766. %K A240767 nonn,hard,more %O A240767 1,1 %A A240767 _Derek Orr_, Apr 12 2014