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 A287219 The numbers which are of the form (a*100 + b*10 + c)*(d*10 + e) = (f*10 + g)*(h*10 + i) (a, b, ... , i are nine digits, 1, 2, ... , 9). 0
 3634, 3726, 3886, 4002, 4234, 4662, 5022, 5056, 5568, 7008, 7448 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Dudeney asked the largest number in 1917 and 7448 (= 532 * 14 = 98 * 76) was found in 1971. REFERENCES Henry Ernest Dudeney, Amusements in Mathematics, 1917. LINKS EXAMPLE Dudeney gave the following example. 158 * 23 = 79 * 46 (= 3634), 158 * 32 = 79 * 64 (= 5056), 174 * 32 = 96 * 58 (= 5568). MATHEMATICA Reap[Do[{a, b, c, d, e, f, g, h, i} = p; m = (a*100 + b*10 + c)*(d*10 + e); If[m == (f*10 + g)*(h*10 + i), Print[m]; Sow[m]], {p, Permutations[ Range[9]]}]][[2, 1]] // Union (* Jean-François Alcover, May 22 2017 *) PROG (Ruby) ary = [] (1..9).to_a.permutation{|a|   i = a[0] * 100 + a[1] * 10 + a[2]   j = a[3] * 10 + a[4]   k = a[5] * 10 + a[6]   l = a[7] * 10 + a[8]   ary << i * j if i * j == k * l } p ary.uniq.sort CROSSREFS Sequence in context: A046835 A143930 A341264 * A232120 A232418 A206844 Adjacent sequences:  A287216 A287217 A287218 * A287220 A287221 A287222 KEYWORD nonn,base,fini,full AUTHOR Seiichi Manyama, May 22 2017 STATUS approved

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Last modified November 28 16:42 EST 2021. Contains 349413 sequences. (Running on oeis4.)