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 A270840 #21 Mar 27 2016 19:23:19 %S A270840 12,36,138,270,546,4800,7560,12840,14700,358200,678480,16139970, %T A270840 22934100,55058580,59553720,74371320,113068380,116605860,242699310, %U A270840 997521210,1592680320,1652749200,3190927740,5088964800,6974736756,9214178820 %N A270840 Numbers n such that n^3 + 1 is a 2-pseudoprime (or Sarrus number). %C A270840 Since n^3 + 1 is clearly composite (n>1), this is n such that 2^(n^3) == 1 (mod n^3+1). %C A270840 There is only one n such that n + 1 is a composite number up to 10^10: 14700. - _Altug Alkan_, Mar 27 2016 %F A270840 a(n) = A265653(n) - 1. - _Altug Alkan_, Mar 24 2016 %o A270840 (PARI) is(n)=Mod(2,n^3+1)^(n^3)==1 %Y A270840 Cf. A001567, A135590, A265653. %K A270840 nonn %O A270840 1,1 %A A270840 _Jeppe Stig Nielsen_, Mar 23 2016 %E A270840 More terms from _Altug Alkan_, Mar 24 2016