A128244 Let s be the sum of the digits of n; a(n) is the product of the digits of s.

1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 3, 4, 5, 6

Offset

1,2

Comments

The sequence is equal to A053837 up to the 488th term.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A007954(A007953(n)). - Michel Marcus, Dec 09 2016

Example

a(345)=2 because 3+4+5=12 and 1*2=2.

Maple

P:=proc(n) local i, k, w; for i from 1 by 1 to n do w:=0; k:=i; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; k:=w; w:=1; while k>0 do w:=w*(k-(trunc(k/10)*10)); k:=trunc(k/10); od; print(w); od; end: P(500);
# alternative
f:= n -> convert(convert(convert(convert(n, base, 10), `+`), base, 10), `*`):
map(f, [$1..100]); # Robert Israel, Dec 09 2016

Mathematica

sdpd[n_]:=Module[{s=Total[IntegerDigits[n]]}, Times@@IntegerDigits[s]]; Array[sdpd, 110] (* Harvey P. Dale, Dec 17 2013 *)

Crossrefs

Cf. A053837, A007953, A007954.

Sequence in context: A292685 A285093 A053837 * A010888 A177274 A349251

Adjacent sequences: A128241 A128242 A128243 * A128245 A128246 A128247

Keyword

easy,nonn,base

Author

Paolo P. Lava and Giorgio Balzarotti, May 03 2007

Extensions

Offset corrected by Robert Israel, Dec 09 2016

Status

approved