A094190 Least n-digit automorphic number.

0, 25, 376, 9376, 90625, 109376, 2890625, 12890625, 212890625, 1787109376, 18212890625, 918212890625, 9918212890625, 40081787109376, 259918212890625, 3740081787109376, 43740081787109376, 256259918212890625, 2256259918212890625

Offset: 1

Author

Lekraj Beedassy, May 25 2004

Keywords

• nonn
• base

Crossrefs

Cf. A003226, A003226, A007185, A016090.

Programs

Mathematica

f[n_] := If[n == 1, 0, Block[{a5 = PowerMod[5, 2^n, 10^n], a6 = PowerMod[16, 5^n, 10^n]}, If[a5 < 10^(n - 1), a5 = 10^(n + 1)]; If[a6 < 10^(n - 1), a6 = 10^(n + 1)]; Min[a5, a6]]]; Array[f, 19] (* Robert G. Wilson v, Aug 27 2006 *)

Formula

a(n) = Min( 5^(2^n) (mod 10^n), 16^(5^n) (mod 10^n) ). - Robert G. Wilson v, Aug 27 2006

Extensions

Corrected and extended by Robert G. Wilson v, Aug 27 2006