login
A228374
Numbers n such that 2*prime(n) - prime(n+1) is not prime.
1
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
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 A374115 A374109
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Aug 21 2013
STATUS
approved