OFFSET
4,1
COMMENTS
The discriminant D of the solution of the Cardano-Tartaglia equation x^3 + p*x + q = 0 is written D = -27*q^2 - 4*p^3. Let q = p = -prime(n) then D = -27*prime(n)^2 - 4*[-prime(n)]^3 = 4*[prime(n)]^3 - 27*prime(n)^2 = (prime(n)^2)*[4*prime(n) - 27], D > 0, n >= 4. a(n) = -D, offset 4,1. Remark: a(1) = -76, a(2) = -135, a(3) = -175.
Because in the preceding comment q can also be taken as +prime(n) this shows that the equation x^3 - prime(n)*x - prime(n) = 0 as well as x^3 - prime(n)*x + prime(p) = 0 has for each n >= 4 three distinct real solutions. - Wolfdieter Lang, Jul 29 2014
LINKS
Freimut Marschner, Table of n, a(n) for n = 4..6320
FORMULA
a(n) = 4*[prime(n)]^3 - 27*prime(n)^2 = (prime(n)^2)*[4*prime(n) - 27], n >= 4.
EXAMPLE
n = 6, prime(6) = 13, 13^2*(4*13 - 27) = 4225.
MATHEMATICA
4#^3-27#^2&/@Prime[Range[4, 40]] (* Harvey P. Dale, Feb 08 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Freimut Marschner, Jul 10 2014
EXTENSIONS
Name and Data have been changed to be in accordance to the Cardano-Tartaglia discriminant.
STATUS
approved