A064454 Erroneous version of A064461.
2, 4, 13, 8, 9, 12, 17, 20
Offset: 0
Keywords
Examples
a(2) = 13 because C(13,5) = 3^2*11*13 and C(13,6) = 2^2*3*11*13.
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a(2) = 13 because C(13,5) = 3^2*11*13 and C(13,6) = 2^2*3*11*13.
a(13) = 2 because C(13,5) = 3^2*11*13 and C(13,6) = 2^2*3*11*13.
f[ n_ ] := (c = 0; k = 1; While[ k < n/2 + .5, If[ Union[ Transpose[ FactorInteger[ Binomial[ n, k ] ] ] [ [ 2 ] ] ] [ [ -1 ] ] > 1, c++ ]; k++ ]; c); Table[ f[ n ], {n, 0, 100} ]
a(n) = sum(k=0, n\2, !issquarefree(binomial(n, k))); \\ Michel Marcus, Mar 05 2014
a(4) = 13 because C(13,5) = C(13,8) = 3^2*11*13 and C(13,6) = C(13,7) = 2^2*3*11*13.
f[ n_ ] := (c = 0; k = 1; While[ k < n, If[ Union[ Transpose[ FactorInteger[ Binomial[ n, k ] ] ] [ [ 2 ] ] ] [ [ -1 ] ] > 1, c++ ]; k++ ]; c); Do[ m = 2; While[ f[ m ] != n, m++ ]; Print[ m ], {n, 0, 6} ]
a(n, v) = {for (i=1, #v, if (v[i] == n, return (i-1));); return (-1);} \\ where v is vector A048277; Michel Marcus, Mar 05 2014
nn = 20; t = Table[-1, {nn}]; found = 0; n = -1; While[found < nn, n++; len = Length[Select[Binomial[n, Range[0, n/2]], SquareFreeQ[#] &]]; If[0 < len <= nn && t[[len]] == -1, t[[len]] = n; found++]]; t
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