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Search: id:A156207
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| A156207 |
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Sum of of the products of the digits in n and their position m in n. |
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+0
1
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| 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 8, 10
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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1,2,3,4,5,6,7,8,9,19 are the only numbers such that a(n) = n. For the
case of a 2-digit number, let 10a+b = a+2b.Then 9a = b so a=1 and b = 9.
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FORMULA
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Given a number n with m digits d1d2d3...dm, a(n) = d1*1+d2*2+d3*3+...+dm*m.
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EXAMPLE
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For n=19 we have 1*1 + 2*9 = 19, the 14-th entry in the sequence.
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PROGRAM
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(PARI) g1(n) = for(j=1, n, print1(g(j)", "))
g(n) = v=Vec((Str(n))); sum(x=1, length(v), x*eval(v[x]))
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CROSSREFS
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Adjacent sequences: A156204 A156205 A156206 this_sequence A156208 A156209 A156210
Sequence in context: A115026 A101337 A135208 this_sequence A061486 A138470 A112875
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KEYWORD
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base,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)hotmail.com), Feb 05 2009, Feb 07 2009
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