A216099 Period of powers of 3 mod 10^n.

4, 20, 100, 500, 5000, 50000, 500000, 5000000, 50000000, 500000000, 5000000000, 50000000000, 500000000000, 5000000000000, 50000000000000, 500000000000000, 5000000000000000, 50000000000000000, 500000000000000000

Offset: 1

Author

V. Raman, Sep 01 2012

Keywords

• nonn
• base
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (10).

Crossrefs

Cf. A000244, A001148, A093143, A001218.

Programs

Mathematica

Table[If[n<5,(4*5^n)/5,10^n/20],{n,20}] (* or *) Join[{4,20,100},NestList[ 10#&,500,20]] (* Harvey P. Dale, May 31 2017 *)

PARI

a(n)=if(n<5,4*5^n/5,10^n/20) \\ Charles R Greathouse IV, Mar 26 2016

Formula

a(n) = 4*5^(n-1) for n <= 4.

a(n) = 5*10^(n-2) for n >= 5.