OFFSET
1,3
EXAMPLE
a(4)=6 because discriminant of quartic x^4+a*x^2+b*x+c is -4*a^3*b^2 - 27*b^4 + 16*a^4*c + 144*a*b^2*c - 128*a^2*c^2 + 256*c^3 that consists of 6 monomials (parts).
MAPLE
1, 1, seq(nops(expand(discrim(x^n + add(c[i]*x^i, i=0..n-2), x))), n=3..12); # Robert Israel, Aug 10 2015
MATHEMATICA
ClearAll[f]; a = {1, 1}; Do[k = 0; Do[If[n > s - 2, If[n > s - 1, k = k + x^n], k = k + f[n] x^n], {n, 0, s}]; m = Resultant[k, D[k, x], x]; AppendTo[a, Length[m]], {s, 3, 8}]; a (* fixed by Vaclav Kotesovec, Mar 20 2019 *)
Flatten[{1, 1, Table[Length[Discriminant[x^n + Sum[Subscript[c, k]*x^k, {k, 0, n-2}], x]], {n, 3, 8}]}] (* Vaclav Kotesovec, Mar 20 2019 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Artur Jasinski, Mar 30 2008
EXTENSIONS
a(2) and Mathematica program corrected [previously had erroneous a(2)=2 because of Length syntax in Mathematica] by Alan Sokal and Andrea Sportiello (sokal(AT)nyu.edu), Jun 17 2010
a(9) to a(12) from Robert Israel, Aug 10 2015
a(13) from Vaclav Kotesovec, Mar 28 2019
STATUS
approved