A074926 Numbers n such that p(n)*p(n+1)+4 is a prime.

2, 11, 18, 40, 47, 51, 74, 76, 91, 96, 97, 105, 108, 164, 185, 203, 205, 208, 227, 238, 243, 252, 271, 291, 312, 321, 349, 351, 362, 374, 392, 396, 406, 420, 438, 449, 453, 523, 529, 541, 562, 576, 590, 602, 629, 639, 641, 668, 679, 698, 711, 720, 734, 752

Offset

1,1

Comments

Primes of form pq+4 where p and q are consecutive primes are in A063442.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

prime(a(n))*prime(a(n)+1)+4 = A063442(n). - Zak Seidov, Oct 03 2013

Example

a(1) = 2 because p(2)*p(3) + 4 = 3*5 + 4 = 19 = A063442(1) prime.
a(2) = 11 because p(11)*p(12) + 4 = 31*37 + 4 = 1151 = A063442(2) prime.

Mathematica

Position[Times@@#+4&/@Partition[Prime[Range[800]], 2, 1], _?PrimeQ]//Flatten (* Harvey P. Dale, Jun 16 2017 *)

Prog

(PARI) isok(n) = isprime(prime(n)*prime(n+1)+4); \\ Michel Marcus, Oct 04 2013

Crossrefs

Cf. A063442.

Sequence in context: A043461 A030551 A121848 * A352932 A066144 A102343

Adjacent sequences: A074923 A074924 A074925 * A074927 A074928 A074929

Keyword

nonn

Author

Zak Seidov, Oct 02 2002

Extensions

Edited according to personal communication of Michel Marcus by Zak Seidov, Oct 03 2013

Status

approved