A169583 n-th prime*8-7 is the square of a prime.

1, 4, 12, 19, 47, 59, 115, 167, 217, 251, 306, 348, 414, 618, 630, 662, 809, 1077, 1138, 1218, 1670, 1876, 2272, 2680, 2869, 3402, 3633, 4242, 4353, 4661, 5255, 6463, 6596, 6986, 8543, 8870, 8992, 9340, 9444, 10265, 11544, 11921, 12449, 13887, 14031

Offset: 1

Author

Juri-Stepan Gerasimov, Mar 01 2010

Keywords

• nonn

Examples

			1 is in the sequence because 1st prime*8-7=(2nd prime)^2;
4 is in the sequence because 4th prime*8-7=(4th prime)^2;
12 is in the sequence because 12th prime*8-7=(7th prime)^2.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..350

Crossrefs

Cf. A000040, A001248, A055469, A118940.

Programs

Mathematica

Select[Range[15000],PrimeQ[Sqrt[8Prime[#]-7]]&] (* Harvey P. Dale, Nov 10 2017 *)

PARI

isok(n) = issquare(sq=prime(n)*8-7) && isprime(sqrtint(sq)); \\ Michel Marcus, Apr 15 2014

Extensions

Corrected (1077 inserted) and extended by R. J. Mathar, Jun 04 2010