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A105661 a(n)=1 if n is a prime, 2 if n is an even semiprime, otherwise 0. 3
0, 1, 1, 2, 1, 2, 1, 0, 0, 2, 1, 0, 1, 2, 0, 0, 1, 0, 1, 0, 0, 2, 1, 0, 0, 2, 0, 0, 1, 0, 1, 0, 0, 2, 0, 0, 1, 2, 0, 0, 1, 0, 1, 0, 0, 2, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 2, 1, 0, 1, 2, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 2, 0, 0, 0, 0, 1, 0, 0, 2, 1, 0, 0, 2, 0, 0, 1, 0, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

EXAMPLE

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

a(4) = 2 because n = 4 = 2*2 is an even semiprime;

a(8) = 0 because n = 8 is neither prime nor an even semiprime.

a(15) = 0 because n = 15 = 3*5 is an odd semiprime.

PROG

(PARI) for(n=1, 105, if((n%2==0)&&(bigomega(n)==2), r=2, r=isprime(n)); print1(r, ", "))

(Scheme) (define (A105661 n) (cond ((= 1 (A001222 n)) 1) ((and (even? n) (= 2 (A001222 n))) 2) (else 0))) ;; Antti Karttunen, Jul 26 2017

CROSSREFS

Cf. A001222, A001751, A105700.

Sequence in context: A226518 A073781 A048622 * A082451 A121362 A234694

Adjacent sequences:  A105658 A105659 A105660 * A105662 A105663 A105664

KEYWORD

easy,nonn

AUTHOR

Giovanni Teofilatto, May 04 2005

EXTENSIONS

Corrected and extended by Rick L. Shepherd, May 17 2005

STATUS

approved

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Last modified October 14 14:34 EDT 2019. Contains 328019 sequences. (Running on oeis4.)