A163769 Primes p such that 2*p+3 is not prime.

3, 11, 23, 31, 37, 41, 59, 61, 71, 79, 83, 101, 103, 107, 109, 131, 149, 151, 163, 179, 181, 191, 211, 233, 239, 241, 251, 257, 263, 271, 281, 293, 311, 313, 317, 331, 347, 359, 367, 373, 389, 401, 419, 421, 431, 433, 443, 449, 457, 461, 479, 491, 499, 521

Offset: 1

Author

Vincenzo Librandi, Aug 04 2009

Keywords

• nonn
• easy

Comments

All those p appear in A144562. [Proof: since 2p+3 is odd and not prime, it can be written as a product of two odd numbers, 2p+3=(2k+1)*(2s+1), therefore p=2ks+k+s-1. - R. J. Mathar, Aug 06 2009]

Examples

			3 is in the sequence because 2*3+3=9 is composite; 23 is in the sequence because 2*23+3=49 is composite.
		

Links

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

Crossrefs

Cf. A144562.

Programs

Magma

[p: p in PrimesUpTo(700) | not IsPrime(2*p+3)]; // Vincenzo Librandi, Apr 08 2013

Mathematica

Select[Prime[Range[200]],!PrimeQ[2#+3]&] (* Harvey P. Dale, Feb 02 2012 *)

Formula

A153238 INTERSECT A000040. - R. J. Mathar, Aug 05 2009

A000040 \ A023204. - R. J. Mathar, Aug 05 2009

Extensions

Entries checked - R. J. Mathar, Aug 06 2009