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.

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.

Links

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

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 *)
ldcQ[n_]:=CompositeQ[Max[Select[Divisors[n], CoprimeQ[#, DivisorSigma[0, n]]&]]]; Select[Range[200], ldcQ] (* Harvey P. Dale, Feb 19 2025 *)

Crossrefs

Cf. A137926, A152444.

Sequence in context: A076349 A175959 A260577 * A161769 A135658 A228589

Adjacent sequences: A152439 A152440 A152441 * A152443 A152444 A152445

Keyword

nonn,changed

Author

Leroy Quet, Dec 04 2008

Extensions

More terms from Stefan Steinerberger and Ray Chandler, Dec 06 2008

Status

approved