A339880 - OEIS

A339880

Odd composite numbers k such that A053575(k) [the odd part of phi] divides k-1.

15, 51, 85, 91, 255, 435, 451, 561, 595, 771, 1105, 1261, 1285, 1351, 1695, 2091, 2431, 2465, 3655, 3855, 4369, 4795, 5083, 5151, 5383, 6601, 6643, 6735, 7051, 8245, 8481, 8695, 8911, 8995, 9061, 9605, 10585, 11155, 13107, 15051, 15211, 16405, 16705, 17733, 18721, 19669, 20451, 21845, 22359, 23001, 26335, 28645

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

OFFSET

1,1

COMMENTS

No common terms with A016105. See A339870 for the reason. - Antti Karttunen, Dec 26 2020

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..1237

MATHEMATICA

q[k_] := OddQ[k] && CompositeQ[k] && Divisible[k-1, (# / 2^IntegerExponent[#, 2])& @ EulerPhi[k]]; Select[Range[30000], q] (* Amiram Eldar, Mar 30 2026 *)

PROG

(PARI)

A000265(n) = (n>>valuation(n, 2));

isA339880(n) = (bitand(n, 1)&&(n>1)&&!isprime(n)&&!((n-1)%A000265(eulerphi(n))));

CROSSREFS

Cf. A000010, A000265, A016105, A053575.

Subsequence of A005117 and of A339879, and of A340077.

Cf. A339869, A339870 (subsequences).

Cf. also A002997, A053576, A339817.

Sequence in context: A238575 A020144 A392922 * A235040 A365473 A075933

Adjacent sequences: A339877 A339878 A339879 * A339881 A339882 A339883

KEYWORD

nonn,changed

AUTHOR

Antti Karttunen, Dec 24 2020

STATUS

approved