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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
OFFSET
1,2
COMMENTS
It might have been more natural to start with index / offset 0. - M. F. Hasler, Jun 24 2016
LINKS
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
Sequence in context: A095197 A333302 A321532 * A046251 A281291 A346644
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