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 A284691 Numbers of the form (10^c-1)*the product any two (not necessarily distinct) terms of A074992. 0
 9, 99, 333, 999, 3663, 9999, 12321, 30303, 36963, 99999, 135531, 333333, 369963, 999999, 1121211, 1367631, 3003003, 3363633, 3699963, 9999999, 12333321, 13688631, 33033033, 33666633, 36999963, 99999999, 102030201, 111111111, 124454421, 136898631, 300030003 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture 1: all terms are palindromic in base 10. Conjecture 2: the sequence A074992 is the maximally dense sequence with this palindromic products property. LINKS EXAMPLE a(3) = 37*9 = 333, with respect to strictly increasing ordering. MATHEMATICA f[n_] := f[n] = (10^(2 n) + 10^n + 1)/3; c[n_] := 10^n - 1; mx = 10^10; i=1; Union@ Reap[ While[c[i] <= mx, j=0; While[c[i] f[j] <= mx, k=0; While[k <= j && (v = c[i] f[j] f[k]) <= mx, Sow@v; k++]; j++]; i++]][[2, 1]] (* Giovanni Resta, Apr 01 2017 *) CROSSREFS Cf. A002283, A074992, A237424. Sequence in context: A292449 A292739 A266022 * A147829 A116274 A116286 Adjacent sequences:  A284688 A284689 A284690 * A284692 A284693 A284694 KEYWORD nonn,base AUTHOR Ahmad J. Masad, Apr 01 2017 EXTENSIONS a(13)-a(31) from Giovanni Resta, Apr 01 2017 STATUS approved

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Last modified August 11 20:13 EDT 2022. Contains 356067 sequences. (Running on oeis4.)