A035004 Number of divisors of the n-th nonprime.

1, 3, 4, 4, 3, 4, 6, 4, 4, 5, 6, 6, 4, 4, 8, 3, 4, 4, 6, 8, 6, 4, 4, 4, 9, 4, 4, 8, 8, 6, 6, 4, 10, 3, 6, 4, 6, 8, 4, 8, 4, 4, 12, 4, 6, 7, 4, 8, 6, 4, 8, 12, 4, 6, 6, 4, 8, 10, 5, 4, 12, 4, 4, 4, 8, 12, 4, 6, 4, 4, 4, 12, 6, 6, 9, 8, 8, 8, 4, 12, 8, 4, 10, 8, 4, 6, 6, 4, 4, 16, 3, 4, 4, 6, 4, 12, 8, 4

Offset: 1

Author

Jason Earls, Jul 05 2001

Keywords

• easy
• nonn

Comments

a(n+1) = a(n) only when a(n) is even. Will these repeat terms include each even integer >= 4? (See also A075036.) - Bill McEachen, Nov 16 2021

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000005, A002808, A018252, A075036.

Programs

Mathematica

DivisorSigma[0,Select[Range[200],!PrimeQ[#]&]] (* Harvey P. Dale, Mar 07 2016 *)

PARI

for(n=1,33, if(!isprime(n), print1(numdiv(n), ", "))) \\ edited by Michel Marcus, Jan 04 2016

Formula

a(n) = A000005(A018252(n)). - Omar E. Pol, Jan 31 2013

Extensions

More terms from Lior Manor, Aug 16 2001