A228519 Numbers n such that sigma(n) = sigma(n - phi(n)), where sigma(n) is the sum of divisors of n and phi(n) is the Euler totient function of n.

9356, 52412, 110442, 160834, 220884, 266866, 289230, 321668, 420790, 441768, 533732, 556818, 578460, 643336, 731530, 841580, 883536, 1067464, 1113636, 1156920, 1286672, 1446150, 1463060, 1683160, 1767072, 2103950, 2134928, 2227272, 2313840, 2545888, 2573344, 2892300

Offset: 1

Author

Paolo P. Lava, Jun 21 2016

Keywords

• nonn
• easy

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010, A000203, A051953, A067880.

Programs

Maple

with(numtheory); P:=proc(q) local n; for n from 1 to q do
if sigma(n)=sigma(n-phi(n)) then print(n); fi; od; end: P(10^9);

Mathematica

Select[Range[10^6], DivisorSigma[1, #] == DivisorSigma[1, # - EulerPhi@ #] &] (* Michael De Vlieger, Jun 21 2016 *)

Formula

sigma(9356- phi(9356)) = sigma(9356 - 4676) = 16380 = sigma(9356).