A228374 Numbers n such that 2*prime(n) - prime(n+1) is not prime.

1, 2, 5, 6, 7, 8, 10, 11, 12, 13, 14, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 38, 39, 41, 42, 43, 44, 45, 46, 48, 49, 50, 52, 53, 54, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 72, 73, 75, 76, 77, 78, 79, 80, 81, 82

Offset: 1

Author

Vincenzo Librandi, Aug 21 2013

Keywords

• nonn
• easy

Comments

Complement of A216075.

Examples

			7 is in the sequence because 2*17-19=15 and 15 is not prime.
		

Links

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

Crossrefs

Cf. A216075.

Programs

Magma

[n: n in [1..100]| not IsPrime(2*NthPrime(n) - NthPrime(n+1))];

Mathematica

f[n_]: = (2 Prime[n] - Prime[n + 1]); Select[Range[110], ! PrimeQ[f[#]]&]
Flatten[Position[2#[[1]]-#[[2]]&/@Partition[Prime[Range[100]],2,1],?(!PrimeQ[#]&)]] (* _Harvey P. Dale, Jan 12 2016 *)