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A336384 Numbers of the form k = x*y where phi(k) = 3*(phi(x) + phi(y)). 1
36, 56, 63, 65, 72, 84, 104, 105, 126, 130, 140, 156, 168, 180, 210 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There are 35 solutions (x, y) to phi(x*y) = 3*(phi(x) + phi(y)): (4, 14), (4, 18), (5, 13), (5, 21), (5, 26), (5, 28), (5, 36), (5, 42), (6, 6), (6, 14), (7, 9), (7, 18), (8, 13), (8, 21), (9, 7), (9, 14), (10, 13), (10, 21), (12, 13), (13, 5), (13, 8), (13, 10), (13, 12), (14, 4), (14, 6), (14, 9), (18, 4), (18, 7), (21, 5), (21, 8), (21, 10), (26, 5), (28, 5), (36, 5), (42, 5).

LINKS

Table of n, a(n) for n=1..15.

GUO Rui, ZHAO Xiqing, ZHANG Lixia and XU Hongxin, The positive integer solutions of euler function phi(mn) = 3^k*(phi(m) + phi(n))

PROG

(PARI) is(k) = fordiv(k, d, if(eulerphi(k) == 3*(eulerphi(d) + eulerphi(k/d)), return(1))); 0;

CROSSREFS

Cf. A000010, A336385.

Sequence in context: A335104 A242343 A243540 * A124941 A116321 A187989

Adjacent sequences:  A336381 A336382 A336383 * A336385 A336386 A336387

KEYWORD

nonn,fini,full

AUTHOR

Jinyuan Wang, Jul 31 2020

STATUS

approved

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Last modified October 15 17:45 EDT 2021. Contains 348033 sequences. (Running on oeis4.)