A120396 - OEIS

%I #9 Aug 28 2021 06:43:16

%S 4,4,1,46,51,197,216,225,366,1862,3806,116

%N a(1) is the least k such that p(1) = (k*17)^2 + k*17 - 1 is prime, then a(n+1) is the least k such that (k*p(n))^2 + k*p(n) - 1 = p(n+1) is prime.

%C The p(n) sequence starts 4691, 352106459, 123978958821625139, ...

%e a(1) = 4 as (4*17)^2 + 4*17 - 1 = 4691 = p(1) is prime.

%t f[0] = {0, 17}; f[n_] := f[n] = Module[{k = 1, p = f[n - 1][[2]]}, While[! PrimeQ[(k*p)^2 + k*p - 1], k++]; {k, (k*p)^2 + k*p - 1}]; Table[f[n][[1]], {n, 1, 10}] (* _Amiram Eldar_, Aug 28 2021 *)

%Y Cf. A120392, A120393, A120394, A120395.

%K nonn

%O 1,1

%A _Pierre CAMI_, Jul 01 2006

%E a(9)-a(12) from _Amiram Eldar_, Aug 28 2021