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A039777
Integers m such that phi(m) is equal to the sum of (the product of prime factors) and (the product of exponents) of m-1.
0
2, 5, 21, 45, 285, 765, 27645, 196605, 41067645, 72787965, 250871805, 4295098365, 12884901885, 23307153405, 172130669565, 1766029428523005, 20978888016396285
OFFSET
1,1
COMMENTS
No other terms below 10^24. Some large terms: 1039619980803100740810795122685, 32576974833437288924302842789885. - Max Alekseyev, Jul 28 2024
All listed terms represent solutions to phi(m) = (m+3)/2 such that (m-1)/2 is an even squarefree number. Cf. A350777. - Max Alekseyev, Jul 21 2024
a(1)=2 is the only even term below 10^100000. - Max Alekseyev, Jul 22 2024
EXAMPLE
21 is a term since 21-1 = 2^2*5^1 and (2*5)+(2*1) = 12 = phi(21).
CROSSREFS
KEYWORD
nonn,more,hard
EXTENSIONS
More terms from Jud McCranie
Corrected example and a(11)-a(14) from Donovan Johnson, Nov 14 2010
a(15)-a(17) from Max Alekseyev, Jul 21 2024
STATUS
approved