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

Author

Paolo P. Lava and Giorgio Balzarotti, May 03 2007

Keywords

• easy
• nonn
• base

Comments

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

Examples

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

Links

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

Crossrefs

Cf. A053837, A007953, A007954.

Programs

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 *)

Formula

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

Extensions

Offset corrected by Robert Israel, Dec 09 2016