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 A081617 #6 Mar 10 2015 12:36:57 %S A081617 1,4,3,10,10,2,1,3,17,13,10,34,38,4,51,55,51,29,68,13,59,30,27,45,18, %T A081617 92,77,82,64,14,68,58,114,68,8,77,42,114,31,98,129,110,43,61,159,35, %U A081617 109,60,91,149,193,2,38,120,259,147,135,22,140,10,263,285,286,134,308 %N A081617 Smallest k such that (product of first n primes)*k+1 is divisible by the (n+1)-th prime. Also (A075306(n)-1)/A002110(n). %e A081617 The 8th prime, 19, divides 2*3*5*7*11*13*17+1=510511, thus a(7)=1. %o A081617 (PARI) for(n=1, 100, p=1; forprime(k=2, prime(n), p=p*k); pn=prime(n+1); s=0; while((s+1)%pn>0, s=s+p); print1(s/p", ")) %Y A081617 Cf. A081618 (positions of unity). %K A081617 nonn %O A081617 1,2 %A A081617 _Ralf Stephan_, Mar 24 2003