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A077807

Number of distinct prime factors of numbers containing in their decimal representation only the digits 0 and 1.

0, 2, 1, 2, 1, 3, 2, 2, 3, 3, 2, 3, 2, 4, 2, 2, 2, 5, 3, 3, 4, 4, 1, 3, 3, 4, 3, 4, 2, 4, 2, 2, 2, 4, 4, 5, 3, 5, 3, 3, 3, 6, 2, 4, 4, 3, 1, 3, 3, 5, 3, 4, 2, 5, 2, 4, 2, 4, 2, 4, 2, 4, 5, 2, 2, 4, 2, 4, 2, 6, 2, 5, 2, 5, 4, 5, 2, 5, 2, 3, 2, 5, 2, 6, 3, 4, 2, 4, 1, 6, 3, 3, 4, 3, 4, 3, 3, 5, 2, 5, 1, 5, 2, 4, 3

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OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

FORMULA

a(n) = A001221(A007088(n)).

EXAMPLE

a(36) = A001221(A007088(36)) = A001221(100100) = A001221(2*2*5*5*7*11*13) = 5.

MATHEMATICA

Table[PrimeNu[FromDigits[IntegerDigits[n, 2]]], {n, 1, 50}] (* G. C. Greubel, May 14 2017 *)

PROG