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 A182253 #27 Jul 31 2017 03:30:16 %S A182253 1,6,8,12,14,15,20,21,24,27,33,38,50,54,57,62,66,69,75,77,78,80,90,99, %T A182253 105,110,111,117,119,138,141,143,147,150,153,155,161,162,164,168,176, %U A182253 188,189,192,194,203,206,209,215,218,231,236,245,246,266,272,278 %N A182253 Nonprime numbers n such that n^2 + n + 1 is prime. %C A182253 All these numbers are in A002384 but not in A053182. %C A182253 The generated prime numbers n^2 + n + 1 are in A185632. %C A182253 All the generated numbers n^2 + n + 1 = 111_n are by definition Brazilian numbers: A125134. See Links: "Les nombres brésiliens" - Section V.5 page 35. %H A182253 Michael De Vlieger, <a href="/A182253/b182253.txt">Table of n, a(n) for n = 1..10000</a> %H A182253 Bernard Schott, <a href="/A125134/a125134.pdf">Les nombres brésiliens</a>, Quadrature, no. 76, avril-juin 2010, pages 30-38; included here with permission from the editors of Quadrature. %t A182253 Select[Range@ 280, And[! PrimeQ@ #, PrimeQ[#^2 + # + 1]] &] (* _Michael De Vlieger_, Jul 30 2017 *) %o A182253 (PARI) isok(n) = ! isprime(n) && isprime(n^2 + n + 1); \\ _Michel Marcus_, Sep 04 2013 %Y A182253 Cf. A002383, A002384, A053182, A053183, A085104, A125134, A185632. %K A182253 nonn %O A182253 1,2 %A A182253 _Bernard Schott_, Dec 18 2012