A139789 Numbers of primes < n-th-prime such that prime(n) + 4 is prime.

0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 19, 19, 19, 19, 19, 20, 20, 20, 20, 20, 21, 21, 21

Offset

1,5

Links

Table of n, a(n) for n=1..78.

Maple

A139789 := proc(n) local a, i; a := 0 ; for i from 1 to n-1 do if isprime(ithprime(i)+4) then a :=a +1 ; fi; od: a ; end: for n from 1 to 100 do printf("%d, ", A139789(n)) ; od: # R. J. Mathar, Oct 05 2008

Mathematica

Join[{0}, Accumulate[Table[If[PrimeQ[n+4], 1, 0], {n, Prime[Range[80]]}]]] (* Harvey P. Dale, Jan 25 2019 *)

Crossrefs

Cf. A082462.

Sequence in context: A179390 A237819 A082447 * A366033 A000720 A230980

Adjacent sequences: A139786 A139787 A139788 * A139790 A139791 A139792

Keyword

nonn

Author

Giovanni Teofilatto, May 21 2008

Extensions

0 added in front, some 6's added and extended by R. J. Mathar, Oct 05 2008

Status

approved