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

1,2

Comments

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

Links

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

Example

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

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 *)

Prog

(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

Crossrefs

Cf. A061582 - A061587.

Sequence in context: A095197 A333302 A321532 * A046251 A281291 A346644

Adjacent sequences: A061578 A061579 A061580 * A061582 A061583 A061584

Keyword

nonn,base,easy

Author

Amarnath Murthy, May 13 2001

Extensions

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

Status

approved