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 A181775 Numbers k such that the decimal digits of k*(k+1) are a permutation of those of k*(k-1). 2
 153, 729, 900, 3420, 4221, 4500, 4779, 4851, 5400, 9153, 13500, 13779, 22500, 24498, 31500, 36927, 40500, 46647, 49221, 49779, 50202, 55152, 61353, 68994, 69894, 77499, 80064, 82872, 83637, 84249, 90495, 102402 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are divisible by 9. - Robert Israel, May 12 2020 LINKS Robert Israel, Table of n, a(n) for n = 1..2500 EXAMPLE 729 is in the sequence because 729*730 = 532170 and 729*728 = 530712. MAPLE filter:= n -> sort(convert(n*(n+1), base, 10))=sort(convert(n*(n-1), base, 10)): select(filter, [seq(i, i=9..200000, 9)]); # Robert Israel, May 11 2020 MATHEMATICA okQ[n_]:=Module[{idn=IntegerDigits[n^2+n]}, Sort[idn]==Sort[IntegerDigits[n^2-n]]]; Select[Range[100000], okQ] PROG (PARI) isok(k) = vecsort(digits(k*(k+1))) == vecsort(digits(k*(k-1))); \\ Michel Marcus, May 12 2020 CROSSREFS Cf. A334798. Sequence in context: A325376 A256740 A199851 * A193249 A050209 A109142 Adjacent sequences: A181772 A181773 A181774 * A181776 A181777 A181778 KEYWORD nonn,base AUTHOR Michel Lagneau STATUS approved

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Last modified April 19 19:02 EDT 2024. Contains 371798 sequences. (Running on oeis4.)