A079702 Numbers 2p where p is prime and 2p + 1 is composite.

14, 26, 34, 38, 62, 74, 86, 94, 118, 122, 134, 142, 146, 158, 194, 202, 206, 214, 218, 254, 274, 278, 298, 302, 314, 326, 334, 362, 386, 394, 398, 422, 446, 454, 458, 482, 514, 526, 538, 542, 554, 566, 614, 622, 626, 634, 662, 674, 694, 698, 706, 734, 746

Offset

1,1

Links

Table of n, a(n) for n=1..53.

Example

7 is prime, 2*7 + 1 = 15 is composite, so a(1) = 7*2 = 14.

Maple

a:=proc(n) if isprime(2*ithprime(n)+1)=false then 2*ithprime(n) else fi end: seq(a(n), n=1..100); # Emeric Deutsch, Jul 25 2006

Mathematica

2Select[Range[375], PrimeQ[#]&&!PrimeQ[2#+1]&] (* Stefano Spezia, Aug 02 2024 *)

Prog

(PARI) forprime (p=3, 200, if (isprime(2*p+1), print1(2*p", ")))

Crossrefs

Cf. A005277.

Equals 2 * A053176.

Sequence in context: A105583 A323030 A005277 * A235688 A176274 A344872

Adjacent sequences: A079699 A079700 A079701 * A079703 A079704 A079705

Keyword

nonn,easy

Author

Jon Perry, Jan 31 2003

Extensions

More terms from Emeric Deutsch, Jul 25 2006

Status

approved