OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..100
EXAMPLE
sigma(4) + phi(4) + d(4) = 7 + 2 + 3 = 12 and sigma(5) + phi(5) + d(5) = 6 + 4 + 2 = 12.
sigma(285) + phi(285) + d(285) = 480 + 144 + 8 = 632 and sigma(286) + phi(286) + d(286) = 504 + 120 + 8 = 632.
MAPLE
with(numtheory): P:=proc(q) local n; for n from 1 to q do
if sigma(n)+phi(n)+tau(n)=sigma(n+1)+phi(n+1)+tau(n+1)
then print(n); fi; od; end: P(10^9);
MATHEMATICA
f[n_] := Module[{fct = FactorInteger[n]}, p = fct[[All, 1]]; e = fct[[All, 2]]; Times @@ (e + 1) + Times @@ ((p^(e + 1) - 1)/(p - 1)) + Times @@ ((p - 1)*p^(e - 1))]; f1 = 0; s = {}; Do[f2 = f[n]; If[f2 == f1, AppendTo[s, n - 1]]; f1 = f2, {n, 2, 10^5}]; s (* Amiram Eldar, Jul 12 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Jun 29 2015
STATUS
approved