OFFSET
1,1
FORMULA
a(n)=Min{x; A077099(x)=n}
EXAMPLE
n=10,a(10)=328, sigma[328]=630,phi[328]=160, sigma(328)+phi(328)=790, sigma(328)-phi(328)=470, GCD[790,470]=10-n; for n=odd number, a[n] should be either a square or twice a square and so quicker search for large values is possible, like e.g. for n=97:a[97]=m=190077688441=435979^2 is the smallest solution.
MATHEMATICA
f[x_] := Apply[GCD, {DivisorSigma[1, x]+EulerPhi[x], DivisorSigma[1, x]-EulerPhi[x]}] t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 10^13}];
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Nov 12 2002
STATUS
approved