A069237 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A069237

Composite n such that tau(n) divides phi(n), where tau(n) is the number of divisors of n and phi(n) the Euler totient function.

8, 9, 10, 15, 18, 21, 24, 26, 28, 30, 33, 34, 35, 39, 40, 45, 49, 51, 52, 55, 56, 57, 58, 63, 65, 69, 70, 72, 74, 76, 77, 78, 82, 84, 85, 87, 88, 90, 91, 93, 95, 98, 99, 102, 104, 105, 106, 108, 110, 111, 115, 117, 119, 120, 122, 123, 124, 125, 126, 128, 129, 130, 133

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Includes A057388 and 2*A002144. - Robert Israel, Jan 05 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

filter:= n -> not isprime(n) and numtheory:-phi(n) mod numtheory:-tau(n)=0:

select(filter, [$4..1000]); # Robert Israel, Jan 05 2018

MATHEMATICA

nn=200; Rest[Select[Complement[Range[nn], Prime[Range[PrimePi[nn]]]], Divisible[ EulerPhi[#], DivisorSigma[0, #]]&]] (* Harvey P. Dale, Mar 31 2011 *)

CROSSREFS

Composite numbers in A003601.

Cf. A002144, A057388.

Sequence in context: A358674 A358675 A091417 * A334728 A070480 A135043

Adjacent sequences: A069234 A069235 A069236 * A069238 A069239 A069240

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Apr 13 2002

STATUS

approved