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

Author

Giovanni Teofilatto, May 04 2005

Keywords

• easy
• nonn

Examples

			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.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 0..10000
• Index entries for sequences computed from exponents in factorization of n

Crossrefs

Cf. A001222, A105661.

Programs

Mathematica

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

Scheme

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

Formula

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