OFFSET
1,2
COMMENTS
LINKS
Paolo P. Lava, Table of n, a(n) for n = 1..1000
EXAMPLE
The arithmetic derivative of 12 is equal to 16 (see A003415). On the other hand the sum of proper divisors of 12 is equal to 16 since 1+2+3+4+6 = 16, so 12 is in the sequence.
MAPLE
with(numtheory);
A212127:=proc(i)
local n, p;
for n from 1 to i do
if sigma(n)/n-1=add(op(2, p)/op(1, p), p=ifactors(n)[2]) then print(n);
fi; od; end:
A212127(1000); # Paolo P. Lava, Jan 04 2012
MATHEMATICA
dn[0] = 0; dn[1] = 0; dn[n_?Negative] := -dn[-n]; dn[n_] := Module[{f = Transpose[FactorInteger[n]]}, If[PrimeQ[n], 1, Plus @@ (n*f[[2]]/f[[1]])]]; Select[Range[300], dn[#] == DivisorSigma[1, #] - # &] (* T. D. Noe, Dec 27 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Dec 18 2012
STATUS
approved