login
A152442
n is included if the largest divisor of n that is coprime to d(n) is a composite, where d(n) is the number of divisors of n.
1
4, 15, 16, 21, 25, 27, 30, 33, 35, 36, 39, 42, 49, 50, 51, 54, 55, 57, 64, 65, 66, 69, 70, 75, 77, 78, 81, 85, 87, 91, 93, 95, 98, 100, 102, 105, 110, 111, 114, 115, 119, 120, 121, 123, 125, 129, 130, 133, 135, 138, 140, 141, 143, 144, 145, 147, 150, 154, 155, 159, 161
OFFSET
1,1
COMMENTS
A137926(a(n)) is composite for all n.
MATHEMATICA
a = {}; For[n = 2, n < 1000, n++, b = Max[Select[Divisors[n], GCD[DivisorSigma[0, n], # ] == 1 &]]; If[b > 1 && ! PrimeQ[b], AppendTo[a, n]]]; a (* Stefan Steinerberger, Dec 06 2008 *)
CROSSREFS
Sequence in context: A076349 A175959 A260577 * A161769 A135658 A228589
KEYWORD
nonn
AUTHOR
Leroy Quet, Dec 04 2008
EXTENSIONS
More terms from Stefan Steinerberger and Ray Chandler, Dec 06 2008
STATUS
approved