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

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.

Mathematica

psp[n_]:=Which[PrimeQ[n], 1, PrimeOmega[n]==2, 2, True, 0]; Join[{0}, Array[ psp, 110]] (* Harvey P. Dale, Sep 18 2011 *)

Prog

(Scheme) (define (A105700 n) (if (< (A001222 n) 3) (A001222 n) 0)) ;; Antti Karttunen, Jul 26 2017

Crossrefs

Cf. A001222, A105661.

Sequence in context: A118829 A118832 A122807 * A366077 A367169 A236831

Adjacent sequences: A105697 A105698 A105699 * A105701 A105702 A105703

Keyword

easy,nonn

Author

Giovanni Teofilatto, May 04 2005

Status

approved