OFFSET
0,4
COMMENTS
a(n) = A097649(n) - 10^n.
phi(10^0+0) = 0, phi(10^1+1)=10 and for n > 0, phi(10^(n+1) + 15*10^n) = 10^(n+1) so for each n, a(n) exists and is less than 25*10^(n-1) + 1. It seems that for n > 0, a(n) mod 10 = 1.
a(11) is greater than 5*10^7.
FORMULA
a[n_]:=(For[m=0, EulerPhi[10^n+m]!=10^n, 1=1, m++ ];m)
EXAMPLE
a(10)=222501 because phi(10^10+222501)=10^10 and for m < 222501 phi(10^10 + m) != 10^10.
MATHEMATICA
a[n_]:=(For[m=0, EulerPhi[10^n+m]!=10^n, 1=1, m++ ]; m); Do[Print[a[n]], {n, 0, 10}]
(* first do *) Needs["DiscreteMath`Combinatorica`"] (* then *) f[n_] := If[n == 0, 1, Block[{p = Select[ Divisors[10^n], PrimeQ[ # + 1] &]}, Min[ Transpose[ Partition[ Flatten[ Table[ Select[ Transpose[{Times @@@ KSubsets[p, i], Times @@@ KSubsets[p + 1, i]}], #[[1]] == 10^n &], {i, 9}]], 2]][[2]] ]]]; Table[ f[n] - 10^n, {n, 0, 23}] (* Robert G. Wilson v, Mar 19 2005 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, Sep 05 2004
EXTENSIONS
More terms from Robert G. Wilson v, Mar 14 2005
STATUS
approved