OFFSET
1,1
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
PROG
(PARI) isok(n) = (nnd = n - numdiv(n)) && !isprime(n) && !((n*(n+1)/2-sigma(n)) % nnd); \\ Michel Marcus, Nov 09 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Nov 07 2013
EXTENSIONS
a(7) from Donovan Johnson, Nov 10 2013
STATUS
approved