A379566 Number of n-digit numbers that have exactly 3 divisors.

2, 2, 7, 14, 40, 103, 278, 783, 2172, 6191, 17701, 51205, 149149, 436932, 1287378, 3809498, 11321211, 33764868, 101029398, 303175579, 912147300, 2750855002, 8313825647, 25176031558, 76375623757, 232082001064, 706304629714, 2152571584249, 6568923555719, 20070705116148

Offset

1,1

Comments

Equivalently, number of n-digit squares of primes. - Stefano Spezia, Mar 15 2026

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..52 (using A122121)

Formula

a(n) = A122121(n) - A122121(n-1).

Mathematica

Table[PrimePi[10^(n/2)]-PrimePi[10^((n-1)/2)], {n, 29}] (* Vincenzo Librandi, Jan 20 2026 *)

Prog

(Magma) [ #PrimesUpTo(Floor(10^(n/2))) - #PrimesUpTo(Floor(10^((n-1)/2))) : n in [1..17] ]; // Vincenzo Librandi, Jan 20 2026

Crossrefs

Column k=3 of A284398.

Cf. A001248, A006880, A122121.

Sequence in context: A162460 A187306 A061274 * A061575 A306009 A290646

Adjacent sequences: A379563 A379564 A379565 * A379567 A379568 A379569

Keyword

nonn,base

Author

Seiichi Manyama, Dec 26 2024

Extensions

a(18)-a(29) from Seiichi Manyama using A122121 data, Dec 26 2024

Status

approved