A063108 a(1) = 1; thereafter a(n+1) = a(n) + product of nonzero digits of a(n).

1, 2, 4, 8, 16, 22, 26, 38, 62, 74, 102, 104, 108, 116, 122, 126, 138, 162, 174, 202, 206, 218, 234, 258, 338, 410, 414, 430, 442, 474, 586, 826, 922, 958, 1318, 1342, 1366, 1474, 1586, 1826, 1922, 1958, 2318, 2366, 2582, 2742, 2854, 3174, 3258, 3498, 4362

Offset: 1

Author

Paul A. Loomis, Aug 08 2001

Keywords

• base
• easy
• nonn
• nice
• look

Comments

Conjecture: no matter what the starting term is, the sequence eventually joins this one. This should be true in any base - base 2, for example, is trivial.

A063114 iterated, beginning with 1. - Reinhard Zumkeller, Jan 15 2012

Examples

			a(2) = 1 + 1 = 2; a(3) = 4; a(6) = 16 + 1*6 = 22; a(22) = 206 + 2*6 = 218.
		

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000
• P. A. Loomis, An Interesting Family of Iterated Sequences
• P. A. Loomis, An Introduction to Digit Product Sequences, J. Rec. Math., 32 (2003-2004), 147-151.
• P. A. Loomis, An Introduction to Digit Product Sequences, J. Rec. Math., 32 (2003-2004), 147-151. [Annotated archived copy]
• Index entries for Colombian or self numbers and related sequences

Crossrefs

Cf. A063112, A063113, A063114, A097050, A051801, A096355, A230102, A232485, A232486, A232487, A232488.

Programs

Haskell

a063108_list = iterate a063114 1  -- Reinhard Zumkeller, Jan 15 2012

Maple

with transforms;
f:=proc(n) option remember; if n=1 then 1
else f(n-1)+digprod(f(n-1)); fi; end;
[seq(f(n),n=1..20)];
# N. J. A. Sloane, Oct 12 2013

Mathematica

f[ n_Integer ] := Block[{s = Sort[ IntegerDigits[ n ]]}, While[ s[[ 1 ]] == 0, s = Drop[ s, 1 ]]; n + Times @@ s]; NestList[ f, 1, 65 ]
nxt[n_]:=n+Times@@Select[IntegerDigits[n],#>0&]; NestList[nxt,1,50] (* Harvey P. Dale, Oct 10 2012 *)

PARI

lista(n)={ my(a=vector(n)); a[1]=1; for(i=1, #a-1, a[i+1] = a[i] + vecprod(select(x->x, digits(a[i])))); a } \\ Harry J. Smith, Aug 18 2009

Formula

A crude heuristic analysis suggests that a(n) grows roughly like (8/9 * (1-y))^(1/(1-y)) * n^(1/1-y) where y = log_10(4.5), i.e., that a(n) ~ 0.033591*n^2.8836.

Extensions

More terms from Robert G. Wilson v, Aug 09 2001