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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
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
KEYWORD
nonn,base
AUTHOR
STATUS
approved

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