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A113939 Numbers k such that sigma(k) and phi(k) are both perfect cubes. 0
1, 300118, 2250885, 5294800, 76336260, 141483384, 242375035, 453280968, 456345036, 461356896, 478240392, 537375930, 1139523375, 1180718238, 1227111595, 1599634410, 5043835125, 5229921340, 5610392513, 6087775939, 6376494509, 11038341720, 11044670824 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
phi(k) = A000010(k) is the Euler totient function, while sigma(k) = A000203(k) is the sum of divisors of k.
Intersection of A020477 and A039771. - Michel Marcus, Jan 04 2014
LINKS
EXAMPLE
sigma(2250885) = 168^3 and phi(2250885) = 96^3.
PROG
(PARI) for(n=1, 10^9, if(ispower(eulerphi(n), 3), if(ispower(sigma(n), 3), print1(n ", ")))) \\ Donovan Johnson, Jan 04 2014
CROSSREFS
Sequence in context: A227700 A050257 A283209 * A023686 A250506 A156998
KEYWORD
nonn
AUTHOR
Giovanni Resta, Jan 31 2006
EXTENSIONS
a(7)-a(20) from Donovan Johnson, Feb 06 2010
a(21)-a(23) from Donovan Johnson, Jan 04 2014
STATUS
approved

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Last modified April 22 09:21 EDT 2024. Contains 371893 sequences. (Running on oeis4.)