OFFSET
1,3
COMMENTS
These are the largest differences between n^2 and sigma(n)*phi(n).
All of the differences are in A069249.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
sigma(10) = 18; phi(10) = 4; 10^2 - sigma(10)*phi(10) = 28. This difference, 28, exceeds the difference for every smaller n, so 28 is in this sequence and 10 is in A164875.
MATHEMATICA
f[n_] := n^2 - EulerPhi[n] * DivisorSigma[1, n]; s = {}; fm = -1; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, fm]], {n, 1, 500}]; s (* Amiram Eldar, Aug 29 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Walter Nissen, Aug 29 2009
EXTENSIONS
a(1) = 0 added by Amiram Eldar, Aug 29 2019
STATUS
approved