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A066531
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EPRNs (Equal Product of Reversible Numbers): numbers which can be expressed as the product of two reversible numbers in at least two different ways.
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10
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2520, 4030, 5740, 7360, 7650, 9760, 10080, 12070, 13000, 14580, 14620, 16120, 17290, 18550, 19440, 22680, 22960, 24300, 25200, 26680, 27010, 29440, 31540, 34780, 36270, 36400, 40300, 40320, 42750, 46060, 49300, 50920, 56050, 57400
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The digital root i.e. ultimate sum of digits of all EPRNs is always 1,4,7 or 9.
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REFERENCES
| S. S. Gupta, EPRNs, Science Today, Feb. 1987, India.
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LINKS
| Hans Havermann, Table of n, a(n) for n = 1..10000
Shyam Sunder Gupta, EPRN Numbers
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EXAMPLE
| 4030 = 130 * 031 = 310 * 013, 144648 = 861 * 168 = 492 * 294, 185472 = 672 * 276 = 384 * 483, 9949716 = 2583 * 3852 = 1476 * 6741, 16746912 = 2556 * 6552 = 4473 * 3744, etc.
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MATHEMATICA
| f[n_] := (r = FromDigits[Reverse[IntegerDigits[n]]]; If[n >= r, n*r, 0]); s = Sort[DeleteCases[Table[f[i], {i, 10^4}], 0]]; Union[s[[Select[Range[Length[s]] - 1, s[[#]] == s[[# + 1]] &]]]]
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CROSSREFS
| Sequence in context: A068547 A094515 A179700 * A159214 A064592 A179722
Adjacent sequences: A066528 A066529 A066530 * A066532 A066533 A066534
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KEYWORD
| base,nonn,changed
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 06 2002
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EXTENSIONS
| Edited by Hans Havermann (gladhobo(AT)teksavvy.com), Feb 11 2012
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