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A141114 Those positive integers n where d(d(n)) is coprime to n, where d(n) is the number of divisors of n. 2
1, 3, 5, 7, 8, 9, 10, 11, 13, 14, 17, 19, 22, 23, 25, 26, 29, 31, 34, 35, 37, 38, 41, 43, 45, 46, 47, 49, 53, 55, 58, 59, 61, 62, 63, 65, 67, 71, 73, 74, 75, 77, 79, 81, 82, 83, 85, 86, 89, 91, 94, 95, 97, 99, 100, 101, 103, 105, 106, 107, 109, 113, 115, 117, 118, 119, 121 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..67.

EXAMPLE

26 has 4 divisors and 4 has 3 divisors. 3 is coprime to 26, so 26 is in the sequence.

MATHEMATICA

Select[Range[200], GCD[DivisorSigma[0, DivisorSigma[0, # ]], # ] == 1 &] (* Stefan Steinerberger, Jun 05 2008 *)

CROSSREFS

Cf. A010553, A141113, A141115.

Sequence in context: A100318 A167707 A131903 * A136443 A247459 A020491

Adjacent sequences:  A141111 A141112 A141113 * A141115 A141116 A141117

KEYWORD

nonn

AUTHOR

Leroy Quet, Jun 04 2008

EXTENSIONS

More terms from Stefan Steinerberger, Jun 05 2008

STATUS

approved

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Last modified December 12 01:57 EST 2019. Contains 329948 sequences. (Running on oeis4.)