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 A270345 #9 Mar 16 2016 17:01:52 %S A270345 4,8,16,24,32,48,64,72,96,120,128,144,168,169,192,216,240,256,264,272, %T A270345 288,336,360,384,385,432,480,504,512,528,544,576,600,648,672,720,768, %U A270345 792,816,840,864,960,961,1008,1024,1056,1080,1088,1105,1121,1152,1176,1200,1296,1320,1344 %N A270345 Composite integers n such that the sum of the Pell numbers A000129(0) + ... + A000129(n-1) is divisible by n. %C A270345 Nonprime terms of A270342. %C A270345 Terms that are not divisible by 4 are 169, 385, 961, 1105, 1121, 3827, 4901, 6265, 6441, 6601, 7107, 7801, 8119, ... %e A270345 4 is a term because 0 + 1 + 2 + 5 = 8 is divisible by 4. %e A270345 8 is a term because 0 + 1 + 2 + 5 + 12 + 29 + 70 + 169 = 288 is divisible by 8. %o A270345 (PARI) a048739(n) = local(w=quadgen(8)); -1/2+(3/4+1/2*w)*(1+w)^n+(3/4-1/2*w)*(1-w)^n; %o A270345 for(n=1, 1e3, if(a048739(n-1) % (n+1) == 0 && !isprime(n+1), print1(n+1, ", "))); %Y A270345 Cf. A000129, A048739, A270342. %K A270345 nonn %O A270345 1,1 %A A270345 _Altug Alkan_, Mar 15 2016