A182434 Number of primes p < n such that 4*p+1 is also prime.

0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8

Offset

1,7

Links

Enrique Pérez Herrero, Table of n, a(n) for n = 1..10000

Formula

a(10^n) = A182265(n).

a(n) = sum(i=2..n, floor(phi(4*i^2+i)/(4*i^2-4*i))). - Enrique Pérez Herrero, May 02 2012.

Mathematica

Accumulate[Table[Boole[PrimeQ[n]&&PrimeQ[4n+1]], {n, 1, 200}]]
Accumulate[If[AllTrue[{#, 4#+1}, PrimeQ], 1, 0]&/@Range[90]] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Feb 26 2015 *)

Crossrefs

Cf. A023212, A182265.

Cf. A005384, A156660, A156874, A092816.

Sequence in context: A208246 A320857 A211664 * A185679 A366721 A080342

Adjacent sequences: A182431 A182432 A182433 * A182435 A182436 A182437

Keyword

nonn

Author

Enrique Pérez Herrero, Apr 28 2012

Status

approved