A082994 Numbers n such that all the following properties hold: (i) n*reverse(n) is a square; (ii) n != reverse(n); (iii) n and reverse(n) are not both squares; and (iv) n and reverse(n) have the same number of digits.
288, 528, 768, 825, 867, 882, 1584, 2178, 4851, 8712, 10989, 13104, 14544, 15984, 20808, 21978, 26208, 27648, 27848, 36828, 40131, 44541, 48139, 48951, 49686, 57399, 68694, 80262, 80802, 82863, 84672, 84872, 87912, 93184, 98901, 99375
Offset: 1
Examples
a(5) = 867 because 867 * 768 = 665856 = 816^2.
References
- C. Stanley Ogilvy and John T. Anderson, Excursions in Number Theory, Oxford University Press, NY. (1966), pp. 88-89.
- J. Earls, Mathematical Bliss, Pleroma Publications, 2009, pages 82-83. ASIN: B002ACVZ6O [From Jason Earls, Nov 22 2009]
Links
- Robert Israel, Table of n, a(n) for n = 1..168
- M. A. Rashid, M. A. Uppal, D. C. B. Marsh and A. Wayne, Product of a Number and Its Reverse, American Mathematical Monthly, vol. 64 (1957), p. 434, E-1243. - _Felix Fröhlich_, Jul 11 2014
Programs
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Maple
revdigs:= proc(n) local L; L:= convert(n,base,10); add(L[-i]*10^(i-1),i=1..nops(L)) end proc: filter:= proc(n) local r; if issqr(n) then return false fi; r:= revdigs(n); r <> n and issqr(r*n) and not issqr(r); end proc: select(filter, [seq(seq(10*i+j,j=1..9),i=1..10^4)]); # Robert Israel, Jun 11 2018
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Mathematica
Select[Range[10^5], And[UnsameQ @@ {#1, #2}, IntegerQ@ Sqrt[#1 #2], AllTrue[{#1, #2}, ! IntegerQ@ Sqrt@ # &], SameQ @@ (IntegerLength@ {#1, #2})] & @@ {#, IntegerReverse@ #} &] (* Michael De Vlieger, Jan 04 2019 *)
Extensions
Name clarified by Bernard Schott, Jan 04 2019
Comments