A171447 Numbers n such that n+1 is prime, and (n+1)^3-n^3 is prime.

1, 2, 4, 6, 10, 28, 30, 42, 52, 58, 66, 88, 108, 136, 156, 172, 196, 238, 312, 346, 352, 388, 448, 520, 546, 556, 570, 576, 598, 612, 646, 676, 732, 742, 786, 856, 906, 940, 976, 1050, 1068, 1092, 1152, 1192, 1222, 1228, 1236, 1302, 1432, 1452, 1458, 1480

Offset: 1

Author

Vincenzo Librandi, Dec 09 2009

Keywords

• nonn
• easy

Examples

			for n=10, 10+1=11 and 11^3-10^3=331; n=28, 28+1=29 and 29^3-28^3=2437
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A165682.

Programs

Magma

[n: n in [1..1500] | IsPrime(n+1) and IsPrime( (n+1)^3-n^3)]; // Vincenzo Librandi, Apr 05 2013

Mathematica

Select[Range[1500], PrimeQ[# + 1]&&PrimeQ[(# + 1)^3 - #^3]&] (* Vincenzo Librandi, Apr 05 2013 *)

PARI

is(n)=isprime(n+1) && isprime(3*n^3+3*n+1) \\ Charles R Greathouse IV, Jun 13 2017

Formula

a(n) = A165682(n)-1. - R. J. Mathar, Jan 04 2011