OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
MATHEMATICA
g[n_] := EulerPhi[ DivisorSigma[1, n]]; f[n_] := f[n] = Block[{lst = NestWhileList[g, n, UnsameQ, All ]}, -Subtract @@ Flatten[ Position[lst, lst[[ -1]]]]]; Select[ Range[599800], f[ # ] == 15 &]
PROG
(PARI) f(x, k=1)=for(i=1, k, x=eulerphi(sigma(x))); x
is(n)=my(t=f(n), h=f(t)); while(t!=h, t=f(t); h=f(f(h))); h=f(h); t!=h && t!=(h=f(h, 2)) && t!=(h=f(h, 2)) && t==f(h, 10) \\ Charles R Greathouse IV, Nov 25 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer and Robert G. Wilson v, Jul 14 2004
STATUS
approved