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Search: id:A117644
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| A117644 |
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Number of different couples of different numbers, with digits different from zero, that produce a sum equal to 10, 100, 1000, 10000, 100000, 1000000, etc. |
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+0
2
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OFFSET
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0,1
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EXAMPLE
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Es. 10 = 1 + 9 = 2 + 8 = 3 + 7 = 4 + 6 therefore we have 4 different couples
9 + 1 is not considered because is the same couple as 1 + 9
5 + 5 is not considered because we consider couples with different numbers
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MAPLE
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P:=proc(n)local i, j, k, ok, count; count:=0; for i from 1 by 1 to n/2-1 do ok:=0; k:=i; while k>0 do j:=frac(k/10)*10; if j=0 then ok:=1; fi; k:=trunc(k/10); od; k:=n-i; while k>0 do j:=frac(k/10)*10; if j=0 then ok:=1; fi; k:=trunc(k/10); od; if ok=1 then count:=count+1; fi; od; print(n/2-1-count); end: P(1000);
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CROSSREFS
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Sequence in context: A120075 A123650 A122910 this_sequence A055602 A073565 A039657
Adjacent sequences: A117641 A117642 A117643 this_sequence A117645 A117646 A117647
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KEYWORD
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nonn
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AUTHOR
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Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), Apr 10 2006
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