login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 1 03:52 EDT 2021. Contains 346384 sequences. (Running on oeis4.)