A254715 Number of n-digit semiprimes with semiprime digits (4, 6, 9).

3, 4, 8, 18, 55, 137, 415, 941, 2854, 7743, 21959, 61545, 175817, 496688

Offset

1,1

Links

Table of n, a(n) for n=1..14.

Formula

a(n) = number of n-digit terms in A107342.

Example

a(1) = 3 because there are 3 one-digit semiprimes with semiprime digits: 4,6,9.
a(2) = 4 because there are 4 two-digit relevant semiprimes: 46,49,69,94.
a(3) = 8 because there are 8 three-digit relevant semiprimes: 446,466,469,649,669,694,699,949.

Crossrefs

Cf. A107342.

Sequence in context: A107429 A372489 A061273 * A107328 A065034 A332707

Adjacent sequences: A254712 A254713 A254714 * A254716 A254717 A254718

Keyword

nonn,base

Author

Zak Seidov, Feb 06 2015

Status

approved