A039777 Integers n such that phi(n) is equal to the sum of (the product of prime factors) and (the product of exponents) of n-1.

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

Offset

1,1

Comments

Next term if it exists is >= 10^8.

a(15) > 3*10^10. - Donovan Johnson

Links

Table of n, a(n) for n=1..14.

Example

phi(21)=12, 20=2^2*5^1, (2*5)+(2*1)=12.

Crossrefs

Cf. A000010, A039696.

Sequence in context: A230656 A266950 A328689 * A246167 A359725 A000941

Adjacent sequences: A039774 A039775 A039776 * A039778 A039779 A039780

Keyword

nonn,hard

Author

Olivier Gérard

Extensions

More terms from Jud McCranie

Corrected example and a(11)-a(14) from Donovan Johnson, Nov 14 2010

Status

approved