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A066531 EPRNs (Equal Product of Reversible Numbers): numbers which can be expressed as the product of two reversible numbers 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 i.e. ultimate sum of digits of all EPRNs 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

STATUS

approved

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Last modified September 24 18:42 EDT 2017. Contains 292433 sequences.