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 A202778 #29 Apr 01 2017 04:57:32
%S A202778 4,1,2,330,10830,25410,8224860,512820,12960606120,434491727670,
%T A202778 1893245380950,71023095613470,878232256181280,11429352906540438870
%N A202778 Least k such that x*k + 1 produces primes for x = 1..n and composite for x = n + 1.
%D A202778 Wacław Sierpiński, Czym sie zajmuje teoria liczb. Warsaw: PW "Wiedza Powszechna", 1957, pp. 88-89.
%t A202778 Table[k = 1; While[i = 1; While[i <= n && PrimeQ[i*k + 1], i++]; i <= n || PrimeQ[i*k + 1], k++]; k, {n, 8}]
%Y A202778 Another version of A088250.
%K A202778 more,nonn
%O A202778 1,1
%A A202778 _Arkadiusz Wesolowski_, Jan 06 2012
%E A202778 a(14) from _Giovanni Resta_, Mar 31 2017