A007668 - OEIS

A007668

Numbers k such that phi(k) divides sigma(k) and sigma(k)/k > sigma(m)/m for all m < k.

1, 2, 6, 12, 840, 332640

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OFFSET

1,2

COMMENTS

a(7) > A004394(10^5) > 10^12146, if it exists. - Amiram Eldar, May 21 2024

LINKS

Table of n, a(n) for n=1..6.

PROG

(PARI) lista(kmax) = {my(f, r, rm = 0); for(k = 1, kmax, f = factor(k); r = sigma(f, -1); if(r > rm, rm = r; if(!(sigma(f) % eulerphi(f)), print1(k, ", ")))); } \\ Amiram Eldar, May 21 2024

CROSSREFS

Intersection of A020492 and A004394.

Sequence in context: A328448 A074180 A126293 * A089415 A282974 A181063

Adjacent sequences: A007665 A007666 A007667 * A007669 A007670 A007671

KEYWORD

nonn

AUTHOR

Walter Nissen

STATUS

approved