A344793 a(n) is the number of primes of the form prime(n) + 2*q where q < prime(n) is prime.

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

Offset

1,4

Links

Robert Israel, Table of n, a(n) for n = 1..5000

Example

a(6) = 3 because with prime(6) = 13 we have 2*2+13 = 17, 2*3+13 = 19 and 2*5+13 = 23 prime.

Maple

f:= proc(n) local i, p;
    p:= ithprime(n);
    numboccur(true, map(isprime, [seq(2*ithprime(i)+p, i=1..n-1)]))
end proc:
map(f, [$1..100]);

Mathematica

a[n_] := Module[{p, q},
  p = Prime[n];
  q = Select[Range[p-1], PrimeQ];
  Count[p + 2 q, _?PrimeQ]];
Table[a[n], {n, 1, 100}] (* Jean-François Alcover, May 16 2023 *)

Crossrefs

Cf. A344794.

Sequence in context: A243339 A244965 A049996 * A143908 A349814 A117572

Adjacent sequences: A344790 A344791 A344792 * A344794 A344795 A344796

Keyword

nonn

Author

J. M. Bergot and Robert Israel, May 28 2021

Status

approved