A107656 - OEIS

A107656

Numbers k such that prime(k) = d(k)*phi(k) + 1, where d(k) is number of positive divisors of k.

1, 2, 3, 4, 652245

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OFFSET

1,2

COMMENTS

There is no further term up to 5*10^7.

a(6) > 10^10, if it exists. - Amiram Eldar, Apr 30 2024

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

652245 is in the sequence because prime(652245) = d(652245)*phi(652245) + 1.

MATHEMATICA

Do[If[Prime[n] == DivisorSigma[0, n]*EulerPhi[n] + 1, Print[n]], {n, 50000000}]

PROG

(PARI) lista(pmax) = {my(k = 0, f); forprime(p=1, 1e16, k++; f = factor(k); if(p == numdiv(f)*eulerphi(f)+1, print1(k, ", "))); } \\ Amiram Eldar, Apr 30 2024

CROSSREFS

Cf. A000005, A000010, A104905, A107657.

Sequence in context: A228311 A258107 A307256 * A330930 A024595 A144804

Adjacent sequences: A107653 A107654 A107655 * A107657 A107658 A107659

KEYWORD

nonn,more

AUTHOR

Farideh Firoozbakht, Jun 06 2005

STATUS

approved