A105700 - OEIS

A105700

a(n)=1 if n is a prime, 2 if n is a semiprime, otherwise 0.

0, 0, 1, 1, 2, 1, 2, 1, 0, 2, 2, 1, 0, 1, 2, 2, 0, 1, 0, 1, 0, 2, 2, 1, 0, 2, 2, 0, 0, 1, 0, 1, 0, 2, 2, 2, 0, 1, 2, 2, 0, 1, 0, 1, 0, 0, 2, 1, 0, 2, 0, 2, 0, 1, 0, 2, 0, 2, 2, 1, 0, 1, 2, 0, 0, 2, 0, 1, 0, 2, 0, 1, 0, 1, 2, 0, 0, 2, 0, 1, 0, 0, 2, 1, 0, 2, 2, 2, 0, 1, 0, 2, 0, 2, 2, 2, 0, 1, 0, 0, 0, 1, 0, 1, 0

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OFFSET

0,5

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..10000

Index entries for sequences computed from exponents in factorization of n

FORMULA

If A001222(n) <= 2, a(n) = A001222(n), otherwise a(n) = 0. - Antti Karttunen, Jul 26 2017

EXAMPLE

a(4) = 1 because n=3 is a prime;

a(5) = 2 because n=4 is a semiprime;

a(9) = 0 because n=8 is not prime neither semiprime.