A067879 Numbers k such that sigma(k) = phi(k*omega(k)+1).

1, 6, 30, 38, 55, 85, 87, 188, 236, 264, 445, 451, 618, 655, 672, 715, 717, 897, 913, 1221, 1265, 1357, 1824, 2095, 2515, 2765, 3009, 3247, 3471, 3605, 3741, 4088, 4117, 4237, 5071, 6747, 7195, 7689, 7701, 8120, 10885, 11577, 12128, 12245, 12549

Offset

1,2

Comments

"Omega(n)" in the definition means the number of distinct prime factors of n, counted without multiplicity. This is implemented in Mathematica as PrimeNu[n] rather than as PrimeOmega[n]. - Harvey P. Dale, Jul 08 2017

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000 (terms 1..200 from Harvey P. Dale)

Mathematica

Select[Range[13000], DivisorSigma[1, #]==EulerPhi[#*PrimeNu[#]+1]&] (* Harvey P. Dale, Jul 08 2017 *)

Prog

(PARI) isok(k) = sigma(k) == eulerphi(k*omega(k)+1); \\ Amiram Eldar, Apr 23 2025

Crossrefs

Cf. A000010 (phi), A000203 (sigma), A001221 (omega).

Sequence in context: A351844 A345265 A062268 * A334900 A136375 A138706

Adjacent sequences: A067876 A067877 A067878 * A067880 A067881 A067882

Keyword

nonn

Author

Benoit Cloitre, Mar 02 2002

Status

approved