A231821 a(n) = mu(n) + 3, where mu is the Mobius function (A008683).

4, 2, 2, 3, 2, 4, 2, 3, 3, 4, 2, 3, 2, 4, 4, 3, 2, 3, 2, 3, 4, 4, 2, 3, 3, 4, 3, 3, 2, 2, 2, 3, 4, 4, 4, 3, 2, 4, 4, 3, 2, 2, 2, 3, 3, 4, 2, 3, 3, 3, 4, 3, 2, 3, 4, 3, 4, 4, 2, 3, 2, 4, 3, 3, 4, 2, 2, 3, 4, 2, 2, 3, 2, 4, 3, 3, 4, 2, 2, 3, 3, 4, 2, 3, 4, 4

Offset: 1

Author

Wesley Ivan Hurt, Nov 13 2013

Keywords

• nonn
• easy

Comments

If n is a prime or a semiprime, a(n) gives the number of divisors of n.

Examples

			a(6) = 4; mu(6) + 3 = 1 + 3 = 4.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..5000
• Index entries for sequences computed from exponents in factorization of n

Crossrefs

Cf. A008683, A228409.

One more than A080847, two more than A007423.

Programs

Maple

with(numtheory); a:=n->mobius(n)+3; seq(a(n), n=1..100);

Mathematica

Table[MoebiusMu[n] + 3, {n, 100}]

PARI

a(n) = moebius(n) + 3; \\ Michel Marcus, Nov 14 2013

Scheme

(define (A231821 n) (+ 3 (A008683 n))) ;; Antti Karttunen, Jul 26 2017