A268576 Composite numbers c such that binomial(2*c-1, c-1)-1 is not squarefree.

9, 25, 27, 39, 49, 81, 104, 117, 121, 125

Offset

1,1

Comments

All terms of A267824 are in the sequence.

Links

Table of n, a(n) for n=1..10.

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

Cf. A228562, A267824.

Sequence in context: A304035 A339726 A155109 * A053850 A225498 A020210

Adjacent sequences: A268573 A268574 A268575 * A268577 A268578 A268579

Keyword

nonn,more

Author

Felix Fröhlich, Feb 21 2016

Extensions

Edited by Max Alekseyev, Sep 13 2023

Status

approved