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A254715 Number of n-digit semiprimes with semiprime digits (4, 6, 9). 1
3, 4, 8, 18, 55, 137, 415, 941, 2854, 7743, 21959, 61545, 175817, 496688 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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: A183494 A107429 A061273 * A107328 A065034 A332707
KEYWORD
nonn,base
AUTHOR
Zak Seidov, Feb 06 2015
STATUS
approved

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Last modified March 2 05:08 EST 2024. Contains 370460 sequences. (Running on oeis4.)