A039777 - OEIS

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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.

2, 5, 21, 45, 285, 765, 27645, 196605, 41067645, 72787965, 250871805, 4295098365, 12884901885, 23307153405, 172130669565, 1766029428523005, 20978888016396285

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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

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

21 is a term since 21-1 = 2^2*5^1 and (2*5)+(2*1) = 12 = phi(21).

CROSSREFS

Cf. A000010, A039696, A350777.

Sequence in context: A230656 A266950 A328689 * A246167 A359725 A000941

Adjacent sequences: A039774 A039775 A039776 * A039778 A039779 A039780

KEYWORD

nonn,more,hard

AUTHOR

Olivier Gérard

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