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A305231
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Numbers that are the product of some integer and its digit reversal.
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4
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0, 1, 4, 9, 10, 16, 25, 36, 40, 49, 64, 81, 90, 100, 121, 160, 250, 252, 360, 400, 403, 484, 490, 574, 640, 736, 765, 810, 900, 976, 1000, 1008, 1089, 1207, 1210, 1300, 1458, 1462, 1600, 1612, 1729, 1855, 1936, 1944, 2268, 2296, 2430, 2500, 2520, 2668, 2701
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OFFSET
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1,3
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COMMENTS
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Terms of A061205, sorted in increasing order, with duplicates removed.
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LINKS
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EXAMPLE
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12*21 = 252, so 252 is a term.
156*651 = 101556, so 101556 is a term. (It can also be written as 273*372; see A203924.)
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MAPLE
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a:= proc(n) option remember; local k, d; for k from 1+a(n-1) do
for d in numtheory[divisors](k) do if k = d*(s-> parse(cat(
seq(s[-i], i=1..length(s)))))(""||d) then return k fi od od
end: a(1):=0:
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MATHEMATICA
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a={0}; h=-1; For[k=0, k<=2701, k++, For[m=1, m<=DivisorSigma[0, k], m++, d=Divisors[k]; If[k/Part[d, m] == FromDigits[Reverse[IntegerDigits[Part[d, m]]]] && k>h , AppendTo[a, k]; h=k]]]; a (* Stefano Spezia, Jan 28 2023 *)
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PROG
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(PARI) isok(n) = if (n==0, return (1), fordiv(n, d, if (n/d == fromdigits(Vecrev(digits(d))), return (1))); return (0)); \\ Michel Marcus, May 28 2018
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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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