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 A066531 Numbers which can be expressed as the product of a number and its reversal in at least two different ways. 11
 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; text; internal format)
 OFFSET 1,1 COMMENTS The digital root of these terms is always 1,4,7 or 9. REFERENCES S. S. Gupta, EPRNs, Science Today, Feb. 1987, India. LINKS Hans Havermann, Table of n, a(n) for n = 1..10000 Shyam Sunder Gupta, EPRN Numbers 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. 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]] &]]]] CROSSREFS Sequence in context: A068547 A094515 A179700 * A258540 A159214 A224542 Adjacent sequences:  A066528 A066529 A066530 * A066532 A066533 A066534 KEYWORD base,nonn AUTHOR Robert G. Wilson v, Jan 06 2002 EXTENSIONS Edited by Hans Havermann, Feb 11 2012 Definition rewritten by N. J. A. Sloane, Aug 01 2019 STATUS approved

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Last modified March 30 16:13 EDT 2020. Contains 333127 sequences. (Running on oeis4.)