A163634 a(n) = (p*(p+4)+1)/2 where (p,p+4) are the n-th cousin prime pair.

11, 39, 111, 219, 759, 1011, 2379, 3279, 4899, 5511, 6159, 8319, 13611, 19011, 25311, 26679, 38919, 47739, 49611, 61599, 72579, 79599, 97239, 105339, 108111, 119559, 125499, 189111, 208011, 227811, 274539, 288039, 297219, 340311, 365511, 370659

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..112

Formula

a(n) = (A143206(n) + 1)/2.

Example

a(1) =  (3* 7 + 1)/2 =  11;
a(2) =  (7*11 + 1)/2 =  39;
a(3) = (13*17 + 1)/2 = 111.

Mathematica

(fQ[n_]:=Block[{fi=FactorInteger@n}, Last@#&/@fi=={1, 1}&&Differences[First@#&/@fi]=={4}]; Select[Range@8000000, fQ] + 1)/2 (* Vincenzo Librandi Jan 02 2018 *)
Join[{11}, (1+Times@@#)/2&/@Select[Partition[Prime[Range[250]], 2, 1], #[[2]]- #[[1]]==4&]] (* Harvey P. Dale, Apr 04 2022 *)

Prog

(Magma) [(p*(p+4)+1)/2: p in PrimesUpTo(1000)| IsPrime(p+4)]; // Vincenzo Librandi, May 17 2014

Crossrefs

Cf. A023200, A046132.

Sequence in context: A162261 A004188 A347477 * A343124 A336901 A173373

Adjacent sequences: A163631 A163632 A163633 * A163635 A163636 A163637

Keyword

nonn

Author

Vincenzo Librandi, Aug 02 2009

Extensions

Entries checked by R. J. Mathar, Aug 07 2009

Status

approved