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

1,2

Comments

Complement of A216075.

Links

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

Example

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

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 *)

Prog

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

Crossrefs

Cf. A216075.

Sequence in context: A182783 A084852 A288659 * A092206 A028746 A028779

Adjacent sequences: A228371 A228372 A228373 * A228375 A228376 A228377

Keyword

nonn,easy

Author

Vincenzo Librandi, Aug 21 2013

Status

approved