A230605 Composite numbers n such that number of non-divisors of n divides sum of non-divisors of n.

4, 18, 20, 24, 432, 588, 692945344

Offset: 1

Author

Jaroslav Krizek, Nov 07 2013

Keywords

• nonn

Comments

a(7) > 10^5.

Composite numbers n such that A231167(n) mod A049820(n) = 0. Complement of primes (A000040) with respect to A140826. Intersection of A002808 and A140826.

The terms 20 and 432 are the only composite numbers < 10^5 that are also terms of A023883.

No more terms up to 10^8. - Michel Marcus, Nov 09 2013

a(8) > 10^11. - Donovan Johnson, Nov 12 2013

a(8) > 4*10^12. - Giovanni Resta, Feb 11 2014

Examples

			20 is in sequence because A024816(20) mod A049820(20) = 168 mod 14 = 0.
		

Crossrefs

Cf. A231167, A000040, A049820, A024816.

Programs

PARI

isok(n) = (nnd = n - numdiv(n)) && !isprime(n) && !((n*(n+1)/2-sigma(n)) % nnd); \\ Michel Marcus, Nov 09 2013

Extensions

a(7) from Donovan Johnson, Nov 10 2013