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Search: id:A156230
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| A156230 |
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Sum of the products of the digits of n and the positions of the digits m in n starting from the last digit. |
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+0
1
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| 1, 2, 3, 4, 5, 6, 7, 8, 9, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Starts to differ from A081594 when n>=100. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 19 2009]
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FORMULA
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Let n = d(1)d(2)...d(m) where d(1),d(2),...,d(m) are the digits of n. Then a(n) = m*d1+(m-1)*d2+...+d(m).
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EXAMPLE
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a(19) = 9*1 + 1*2 = 11.
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PROGRAM
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(PARI) gr(n) = v=Vec((rev(n))); sum(x=1, length(v), x*eval(v[x]))
gr1(n) = for(j=1, n, print1(gr(j)", "))
rev(str) = /* Get the reverse of the input string
*/ {
local(tmp, s, j);
tmp = Vec(Str(str));
s="";
forstep(j=length(tmp), 1, -1,
s=concat(s, tmp[j]));
return(s)
}
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CROSSREFS
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Sequence in context: A138795 A093017 A028897 this_sequence A081594 A038506 A091047
Adjacent sequences: A156227 A156228 A156229 this_sequence A156231 A156232 A156233
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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 06 2009
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EXTENSIONS
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Changed the description, formula and Pari code Cino Hilliard (hillcino368(AT)hotmail.com), Feb 08 2009
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