A396176 a(n) = primepi(A394720(n)).

1, 2, 3, 4, 5, 7, 10, 15, 21, 30, 42, 62, 92, 137, 204, 306, 462, 701, 1066, 1634, 2504, 3842, 5927, 9135, 14132, 21881, 33958, 52779, 82185, 128158, 200065, 312748, 489472, 766792, 1202449, 1887463, 2965181, 4662549, 7337565, 11555256, 18210876, 28719623

Offset

1,2

Comments

This is surprisingly difficult to compute! - N. J. A. Sloane, May 26 2026

Links

Chai Wah Wu, Table of n, a(n) for n = 1..100

Formula

a(n) = A000720(A394720(n)).

Example

A394720(10) = 113 is the 30-th prime, so a(10) = 30.

Maple

b:= proc(n) option remember;
      `if`(n<3, n+1, (s-> ((x, y)-> `if`(y-s<s-x, y, x))(
          prevprime(s+1), nextprime(s-1)))(b(n-1)+b(n-2)))
    end:
a:= n-> numtheory[pi](b(n)):
seq(a(n), n=1..40);  # Alois P. Heinz, May 25 2026

Crossrefs

Cf. A000720, A394720.

Sequence in context: A275174 A282582 A282502 * A212463 A130080 A057496

Adjacent sequences: A396173 A396174 A396175 * A396177 A396178 A396179

Keyword

nonn

Author

N. J. A. Sloane, May 25 2026

Extensions

a(31)-a(42) from Alois P. Heinz, May 25 2026

Status

approved