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]] &]]]]
Take[Select[Tally[Table[If[n<IntegerReverse[n], Nothing, n IntegerReverse[ n]], {n, 5000}]], #[[2]]>1&][[All, 1]]//Union, 40] (* Harvey P. Dale, Aug 28 2021 *)
CROSSREFS
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