OFFSET
1,1
COMMENTS
Tested up to n = 10^6.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..228 (terms < 3*10^10)
EXAMPLE
phi(172) = 84, sigma(172) = 308, sigma(84) = 224 and 308 - 84 = 224.
MAPLE
with(numtheory); P:=proc(q) local n;
for n from 1 to q do
if sigma(phi(n))=sigma(n)-phi(n) then print(n);
fi; od; end: P(10^6);
MATHEMATICA
dpQ[n_]:=Module[{p=EulerPhi[n]}, DivisorSigma[1, p]==DivisorSigma[1, n]-p]; Select[Range[12*10^6], dpQ] (* Harvey P. Dale, Apr 27 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Oct 17 2013
STATUS
approved