A352580 Numbers k such that A001414(k)*A001414(k+1)+A001414(k)+A001414(k+1) is prime.

1, 2, 3, 4, 6, 13, 14, 18, 19, 20, 23, 24, 28, 38, 40, 42, 44, 45, 48, 52, 53, 63, 68, 80, 81, 83, 87, 88, 89, 90, 91, 94, 95, 99, 106, 107, 109, 112, 118, 121, 122, 123, 133, 134, 135, 137, 145, 146, 148, 149, 153, 158, 159, 162, 164, 166, 173, 175, 176, 179, 183, 184, 188, 196, 202, 207, 209

Offset: 1

Author

J. M. Bergot and Robert Israel, Mar 21 2022

Keywords

• nonn

Comments

Numbers k such that (A001414(k)+1)*(A001414(k+1)+1)-1 is prime.

Examples

			a(5)=6 is a term because A001414(6) = 2+3 = 5, A001414(7) = 7, and 5*7+5+7 = 47 is prime.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001414.

Programs

Maple

spf:= proc(n) local t; add(t[1]*t[2],t=ifactors(n)[2]) end proc:
select(t -> isprime((spf(t)+1)*(spf(t+1)+1)-1), [$1..1000]);