cp's OEIS Frontend

A308988 a(n) = A293564(n) - 1.

%I A308988 #14 Aug 03 2019 22:06:57
%S A308988 1,2,6,26,40,94,184,350,496,3390,3536,45370,82734,99064,357164,840904,
%T A308988 3880556,27914936,40517520,104715206,1126506904,2084910530,2442825346,
%U A308988 4332318176,6716598046,17736392220,18205380336,30869303806,68506021364,78491213264,85620067844
%N A308988 a(n) = A293564(n) - 1.
%C A308988 The value of n such that a new record number of composites appear for (n+1)^2+1, (n+2)^2+1, (n+3)^2+1, ...
%C A308988 Corresponding record gap sizes are given in A308987.
%e A308988 n=6   -->  6^2+1 = 37, prime
%e A308988 n=7   -->  7^2+1 = 50, composite
%e A308988 n=8   -->  8^2+1 = 65, composite
%e A308988 n=9   -->  9^2+1 = 82, composite
%e A308988 n=10  -->  10^2+1 = 101, prime
%e A308988 ...yields the third record gap number of terms, so the start index n=6 appears as the third entry in this sequence.
%t A308988 best = c = lastBestAt = 0;
%t A308988 For[i = 2, True, i += 2; c += 2,
%t A308988 If[PrimeQ[i^2 + 1],
%t A308988    If[c > best,
%t A308988     best = c;
%t A308988     bestAt = i - c;
%t A308988     If[bestAt != lastBestAt, Print[{c, bestAt}]];
%t A308988     lastBestAt = bestAt;
%t A308988     ];
%t A308988    c = 0;
%t A308988    ]
%t A308988 ]
%Y A308988 Cf. A002496, A002522, A293564, A308987.
%K A308988 nonn
%O A308988 1,2
%A A308988 _Trevor Cappallo_, Jul 04 2019
%E A308988 a(21)-a(31) from _Giovanni Resta_, Jul 05 2019