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A268576
Composite numbers c such that binomial(2*c-1, c-1)-1 is not squarefree.
0
9, 25, 27, 39, 49, 81, 104, 117, 121, 125
OFFSET
1,1
COMMENTS
All terms of A267824 are in the sequence.
MATHEMATICA
Select[Range[200], CompositeQ[#]&&!SquareFreeQ[Binomial[2#-1, #-1]-1]&] (* Harvey P. Dale, Jul 31 2023 *)
PROG
(PARI) forcomposite(c=1, , if(!issquarefree(binomial(2*c-1, c-1)-1), print1(c, ", ")))
(Magma) [n: n in [2..125] | not IsPrime(n) and not IsSquarefree(Binomial(2*n-1, n-1) - 1)]; // Vincenzo Librandi, Feb 25 2016
CROSSREFS
Sequence in context: A304035 A339726 A155109 * A053850 A225498 A020210
KEYWORD
nonn,more
AUTHOR
Felix Fröhlich, Feb 21 2016
EXTENSIONS
Edited by Max Alekseyev, Sep 13 2023
STATUS
approved