A238097 Number of monic cubic polynomials with coefficients from {1..n} and maximum coefficient equal to n, for which all three roots are integers.
0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 2, 1, 1, 1, 2, 1, 2, 0, 2, 2, 2, 0, 3, 2, 1, 2, 3, 1, 3, 0, 3, 3, 1, 1, 4, 3, 1, 1, 3, 2, 3, 1, 2, 3, 2, 0, 4, 5, 2, 2, 2, 1, 3, 3, 3, 3, 1, 0, 5, 4, 1, 2, 4, 4, 3, 1, 2, 2, 3, 1, 5, 6, 1, 2, 3, 2, 3, 1, 4, 6, 2, 0, 5, 5, 1, 1, 3
Offset: 1
Keywords
Examples
a(11) = 2 with polynomials x^3 + 6*x^2 + 11*x + 6 = (x+1) * (x+2) * (x+3) and x^3 + 7*x^2 + 11*x + 5 = (x+1)^2 * (x+5). - _Michael Somos_, Feb 23 2014
Links
- Zak Seidov, Table of n, a(n) for n = 1..1000
- Dorin Andrica and Eugen J. Ionascu, On the number of polynomials with coefficients in [n], An. St. Univ. Ovidius Constanta, Vol. 22(1),2014, 13-23.
Programs
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Mathematica
Table[p = Flatten[Table[{a, b, c, 1}, {a, n}, {b, n}, {c, n}], 2]; cnt = 0; Do[If[Max[p[[i]]] == n, poly = p[[i]].x^Range[0, 3]; r = Rest[FactorList[poly]]; If[Total[Transpose[r][[2]]] == 3 && Union[Coefficient[Transpose[r][[1]], x]] == {1}, Print[{n, r}]; cnt++]], {i, Length[p]}]; cnt, {n, 20}] (* T. D. Noe, Feb 22 2014 *) -
PARI
{a(n) = if( n<1, 0, sum(a1=1, n, sum(a2=1, n, sum(a3=1, n, vecmax([a1, a2, a3]) == n && vecsum( factor( Pol([1, a1, a2, a3]))[, 2]) == 3))))}; /* Michael Somos, Feb 23 2014 */
Extensions
Definition corrected by Giovanni Resta, Feb 22 2014
Extended by T. D. Noe, Feb 22 2014
Comments