login
A058653
Numbers k such that sigma(phi(k)) = phi(sigma(k)-k).
0
2, 18, 50, 1250, 1980, 6900, 61080, 1369020, 2025660, 2820240, 4003230, 4917360, 8597316, 15396360, 15893010, 28725648, 41427360, 53423760, 148663020, 209752500, 212019024, 222746160, 232210080, 281870316, 298848144, 314121180, 322230180, 385612260, 390760260
OFFSET
1,1
MATHEMATICA
Select[ Range[ 10^6 ], DivisorSigma[ 1, EulerPhi[ # ] ] == EulerPhi[ DivisorSigma[ 1, # ] - # ] & ]
PROG
(Python)
from sympy import divisor_sigma as sigma, totient as phi
def aupto(limit):
for k in range(2, limit):
if sigma(phi(k)) == phi(sigma(k) - k): print(k, end=", ")
aupto(10**4) # Michael S. Branicky, Feb 18 2021
CROSSREFS
Cf. A062402.
Sequence in context: A356712 A077591 A050808 * A058794 A114109 A085293
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Dec 26 2000
EXTENSIONS
a(8)-a(29) from Donovan Johnson, Jan 19 2012
STATUS
approved