A061581 a(1) = 1, a(n) = number obtained by replacing each digit of a(n-1) with its double.

1, 2, 4, 8, 16, 212, 424, 848, 16816, 21216212, 424212424, 848424848, 1681684816816, 212162121681621216212, 42421242421216212424212424, 848424848424212424848424848, 16816848168168484248481681684816816

Offset: 1

Author

Amarnath Murthy, May 13 2001

Keywords

• nonn
• base
• easy

Comments

It might have been more natural to start with index / offset 0. - M. F. Hasler, Jun 24 2016

Examples

			The term after 16 is 2.12, i.e., 212.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..29

Crossrefs

Cf. A061582 - A061587.

Programs

Maple

a:= proc(n) option remember; `if`(n=1, 1, (l->
       parse(cat(seq(2*l[-i], i=1..nops(l)))))(
             convert(a(n-1), base, 10)))
    end:
seq(a(n), n=1..20);  # Alois P. Heinz, Jun 24 2016

Mathematica

NestList[FromDigits[Flatten[IntegerDigits[2*IntegerDigits[#]]]] &,1,16] (* Jayanta Basu, May 20 2013 *)

PARI

A061581(n=2,a=1,m=2)={while(n--,a=eval(concat(apply(t->Str(t),digits(a)*m))));a} \\ If only the 2nd argument is given, then the operation is applied once to that argument. - M. F. Hasler, Jun 24 2016

Extensions

More terms from Larry Reeves (larryr(AT)acm.org) and Asher Auel, May 15 2001