A138908 a(n) = d^d, where d is the number of digits in n.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27

Offset: 0

Author

Odimar Fabeny, May 16 2008

Keywords

• easy
• nonn
• base

Crossrefs

Cf. A055642, A138902, A308314.

Programs

Mathematica

dd[n_]:=Module[{d=IntegerLength[n]},d^d]; Join[{1},Array[dd,150]] (* Harvey P. Dale, Mar 16 2013 *)

PARI

a(n) = my(d=#Str(n)); d^d; \\ Michel Marcus, Nov 18 2020

Formula

From Amiram Eldar, Nov 18 2020: (Start)

a(n) = A055642(n)^A055642(n).

Sum_{n>=1} 1/a(n) = A308314. (End)

Extensions

Edited by N. J. A. Sloane, Sep 29 2011, at the suggestion of Franklin T. Adams-Watters