A055696 Numbers k such that k | sigma_2(k) + phi(k)^2.

1, 2, 6, 182, 330, 850, 2150, 5964, 23028, 85800, 168150, 172250, 179850, 308700, 391300, 484692, 507725, 1098750, 1248148, 1377075, 3105218, 4723500, 9547650, 17353350, 22058792, 37465350, 47094425, 54658450, 110019000, 144820200, 194860380, 199728900, 203687250, 238625100

Offset

1,2

Links

Table of n, a(n) for n=1..34.

Mathematica

Do[If[Mod[DivisorSigma[2, n]+EulerPhi[n]^2, n]==0, Print[n]], {n, 1, 2*10^6}]

Prog

(PARI) isok(k) = {my(f = factor(k)); !((sigma(f, 2) + eulerphi(f)^2) % k); } \\ Amiram Eldar, Feb 16 2026

Crossrefs

Cf. A000010 (phi), A001157 (sigma_2).

Sequence in context: A203430 A298883 A252740 * A380475 A158096 A345726

Adjacent sequences: A055693 A055694 A055695 * A055697 A055698 A055699

Keyword

nonn

Author

Robert G. Wilson v, Jun 09 2000

Extensions

a(21)-a(30) from Donovan Johnson, Feb 13 2010

a(31)-a(34) from Amiram Eldar, Feb 16 2026

Status

approved