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 A158942 #27 Dec 13 2015 07:12:07 %S A158942 3,7,11,13,17,19,21,23,27,29,31,33,37,39,41,43,47,51,53,57,59,61,63, %T A158942 67,69,71,73,77,79,83,87,89,91,93,97,99,101,103,107,109,111,113,117, %U A158942 119,123,127,129,131,133,137,139,141,143,147,149,151,153,157,159,161,163 %N A158942 Nonsquares coprime to 10. %C A158942 Odd primes + odd nonprime integers that have an odd numbers of proper divisors A082686, are the result of a suppression of integers satisfying: 2n (A005843); n^2 (A000290); n^2+n (A002378). Of these, we can suppress the multiples of 5 (A008587). %C A158942 Decimal expansion of 1/10^(n^2+n) + 1/10^(n^2) + 1/10^(5*n) + 1/10^(2*n) gives a 0 for these integers. %C A158942 2n + n(n+1) + n^2 = 2n^2 + 3n = A014106. %C A158942 2n^2 + 3n + 5n = 2n^2 + 8n = 2n(n+4) = A067728 8(8+n) is a perfect square. %H A158942 Charles R Greathouse IV, <a href="/A158942/b158942.txt">Table of n, a(n) for n = 1..10000</a> %t A158942 Select[Range@ 163, ! IntegerQ@ Sqrt@ # && CoprimeQ[#, 10] &] (* _Michael De Vlieger_, Dec 11 2015 *) %o A158942 (PARI) isok(n) = (n % 2) && (n % 5) && (isprime(n) || (numdiv(n) % 2 == 0)); \\ _Michel Marcus_, Aug 27 2013 %o A158942 (PARI) is(n)=gcd(n,10)==1 && !issquare(n) \\ _Charles R Greathouse IV_, Sep 05 2013 %Y A158942 Intersection of A000037 and A045572. %Y A158942 Cf. A082868, A002378, A000290, A005843, A008587, A014106, A067728. %K A158942 nonn,easy %O A158942 1,1 %A A158942 _Eric Desbiaux_, Mar 31 2009 %E A158942 New name from _Charles R Greathouse IV_, Sep 05 2013