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 A260868 #7 Aug 11 2015 12:38:29 %S A260868 89,173,179,229,269,439,499,509,523,557,577,599,619,677,719,769,797, %T A260868 839,859,929,1009,1013,1031,1049,1061,1069,1109,1129,1217,1223,1237, %U A260868 1259,1279,1291,1303,1319,1447,1471,1483,1489,1499,1523,1559,1579,1601,1609,1667,1699,1709,1721,1783,1789,1811,1879,1889,1931,1933 %N A260868 Numbers for which the least k > 1 which divides n + 2^k - 2 is different from the smallest prime factor of n. %C A260868 Somewhat astonishingly, n = 89 is the only number below 173 for which the least prime factor is different from the least k > 1 which divides n + 2^k - 2. For larger n, this property becomes more frequent. %C A260868 The first composite number in this sequence is a(105) = 3239. %o A260868 (PARI) my(aa(n)=for(k=2,9e9,Mod(2,k)^k+n-2||return(k)));for(n=2,1e5,aa(n)!=factor(n)[1,1]&&print1(n",")) %K A260868 nonn %O A260868 1,1 %A A260868 _M. F. Hasler_, Aug 11 2015