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A128244 Let s be the sum of the digits of n; a(n) is the product of the digits of s. 1
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 (list; graph; refs; listen; history; text; internal format)
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 A131650

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

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Last modified October 20 05:31 EDT 2018. Contains 316378 sequences. (Running on oeis4.)