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Search: id:A136025
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| A136025 |
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Sum of distinct prime factors of odd N <= 10^n-1 (excluding unity and the value of N itself). |
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1
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OFFSET
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1,1
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COMMENT
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Through n^5 about 37.5 percent of total sums for all N comprise sums of odd N and the remaining 62.5 percent to even N.
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FORMULA
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Compute distinct prime factors, without repetition, of each odd N; sum the total <= each successive power of 10 (beginning with 10^1-1).
a(n) = sum_{k=1,2,...,A093143(n)} A105221(2k-1). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 29 2008
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EXAMPLE
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a(0)=3 because the only odd N <=10^1-1 having a prime factor is 9 and its factor is 3 and sum is 3.
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MAPLE
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A105221 := proc(n) local a, ifs, p; ifs := ifactors(n)[2] ; a := 0 ; for p in ifs do if op(1, p) <> 1 and op(1, p) <> n then a := a+op(1, p) ; fi ; od: RETURN(a) ; end: A136025 := proc(n) local a, k ; a := 0 ; for k from 5 to 10^n-1 by 2 do a := a+A105221(k) ; od: RETURN(a) ; end: for n from 1 do print(A136025(n)); od: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 29 2008
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CROSSREFS
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Cf. A136021, A136024.
Sequence in context: A062226 A110717 A068988 this_sequence A157577 A062604 A160192
Adjacent sequences: A136022 A136023 A136024 this_sequence A136026 A136027 A136028
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KEYWORD
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more,nonn
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Dec 12 2007
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EXTENSIONS
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a(6) from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 29 2008
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