A077809 - OEIS

A077809

Number of divisors of numbers containing in their decimal representation only the digits 0 and 1.

1, 4, 2, 9, 2, 8, 4, 16, 8, 8, 4, 18, 4, 16, 4, 25, 4, 32, 8, 18, 16, 16, 2, 32, 8, 16, 12, 36, 4, 16, 4, 36, 4, 16, 16, 72, 8, 32, 8, 32, 8, 64, 4, 36, 16, 8, 2, 50, 8, 32, 8, 36, 4, 48, 4, 64, 4, 16, 4, 36, 4, 16, 32, 49, 4, 16, 4, 36, 4, 64, 4, 128, 4, 32, 16, 72, 4, 32, 4, 50, 4, 32, 6

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OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A000005(A007088(n)).

EXAMPLE

a(6) = A000005(A007088(6)) = A000005(110) = 8, as 110 has divisors: 1, 2, 5, 10, 11, 22, 55 and 110.

MATHEMATICA

With[{z1=Rest[FromDigits/@Tuples[{0, 1}, 7]]}, DivisorSigma[0, #]&/@z1] (* Harvey P. Dale, Sep 19 2021 *)

PROG