A179887 - OEIS

A179887

Nonprimes q such that antiharmonic mean B(q) of the numbers k < q such that gcd(k, q) = 1 is integer, where B(q) = A053818(q) / A023896(q) = A175505(q) / A175506(q).

1, 10, 22, 34, 46, 55, 58, 82, 85, 91, 94, 106, 110, 115, 118, 133, 142, 145, 166, 170, 178, 182, 187, 202, 205, 214, 217, 226, 230, 235, 247, 253, 259, 262, 265, 266, 274, 290, 295, 298, 301, 319, 334, 346, 355, 358, 374, 382, 391, 394, 403, 410, 415, 427

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OFFSET

1,2

COMMENTS

Nonprimes q such that A175506(q) = 1. Subsequence of A179871. Union a(n) and A003627 = A179871. Corresponding values of B(q) in A179890.

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1653

EXAMPLE

a(6) = 55 because B(55) = A053818(55) / A023896(55) = 40700 / 1100 = 37 (integer).

MATHEMATICA

f[n_] := 2 Plus @@ (Select[ Range@n, GCD[ #, n] == 1 &]^2)/(n*EulerPhi@n); Select[ Range@ 433, ! PrimeQ@# && IntegerQ@ f@# &] (* Robert G. Wilson v, Aug 02 2010 *)

CROSSREFS

Cf. A179871, A179872, A179873, A179874, A179875, A179876, A179877, A179878, A179879, A179880, A179882, A179883, A179884, A179885, A179887, A179890, A179891.

Sequence in context: A109958 A053361 A214153 * A339003 A017641 A232540

Adjacent sequences: A179884 A179885 A179886 * A179888 A179889 A179890

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Jul 30 2010, Jul 31 2010

EXTENSIONS

More terms from Robert G. Wilson v, Aug 02 2010

STATUS

approved