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A061581 a(1) = 1, a(n) = number obtained by replacing each digit of a(n-1) with its double. 20
1, 2, 4, 8, 16, 212, 424, 848, 16816, 21216212, 424212424, 848424848, 1681684816816, 212162121681621216212, 42421242421216212424212424, 848424848424212424848424848, 16816848168168484248481681684816816 (list; graph; refs; listen; history; text; internal format)
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 A164312

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 Natan Auel (auela(AT)reed.edu), May 15 2001

STATUS

approved

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Last modified June 21 07:27 EDT 2021. Contains 345358 sequences. (Running on oeis4.)