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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.
1
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
1,1
LINKS
FORMULA
sigma(9356- phi(9356)) = sigma(9356 - 4676) = 16380 = sigma(9356).
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 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Jun 21 2016
STATUS
approved