A072585 - OEIS

A072585

Numbers k such that k and phi(k) end with the same digit in base 10.

1, 38, 42, 50, 58, 76, 84, 100, 102, 110, 116, 118, 126, 150, 152, 158, 168, 178, 182, 200, 204, 218, 220, 222, 232, 236, 250, 252, 278, 282, 294, 298, 300, 304, 306, 310, 316, 322, 330, 336, 350, 356, 358, 364, 378, 398, 400, 402, 408, 410, 436, 440, 442

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

OFFSET

1,2

COMMENTS

Numbers k such that the cototient of k is divisible by 10. - Darío Clavijo, Apr 04 2023

LINKS

Table of n, a(n) for n=1..53.

FORMULA

Probably lim n -> infinity a(n)/n = 10.

PROG

(PARI) isok(n) = (n % 10) == (eulerphi(n) % 10); \\ Michel Marcus, Nov 26 2013

(Python)