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A122481
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a(n) = if n < 10 then n else a(digitsum(n)) + digitsum(n), where digitsum(n)=A007953(n), the sum of digits in decimal representation of n.
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1
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 2, 4, 6, 8, 10, 12, 14, 16, 18, 12, 4, 6, 8, 10, 12, 14, 16, 18, 12, 15, 6, 8, 10, 12, 14, 16, 18, 12, 15, 18, 8, 10, 12, 14, 16, 18, 12, 15, 18, 21, 10, 12, 14, 16, 18, 12, 15, 18, 21, 24, 12, 14, 16, 18, 12, 15, 18, 21, 24, 27, 14, 16, 18, 12, 15, 18
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listen;
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OFFSET
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0,3
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LINKS
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EXAMPLE
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a(49)=a(4+9)+(4+9)=a(13)+13=a(1+3)+(1+3)+13=a(4)+4+13=4+4+13=21.
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MAPLE
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ds := proc(n) local t1, t2; t1 := n; t2 := 0; while t1 <> 0 do t2 := t2 + (t1 mod 10); t1 := floor(t1/10); od: t2; end;
M:=10000; a:=array(0..M); for n from 0 to 9 do a[n]:=n; lprint(n, a[n]); od: for n from 10 to M do a[n]:=a[ds(n)]+ds(n); lprint(n, a[n]); od:
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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