A348728 Decimal expansion of the absolute value of one of the negative roots of Shanks' simplest cubic associated with the prime p = 37.

1, 1, 8, 7, 1, 0, 0, 8, 0, 7, 6, 0, 6, 4, 0, 9, 2, 0, 1, 6, 8, 3, 3, 7, 0, 0, 9, 8, 7, 2, 2, 7, 6, 1, 0, 9, 9, 3, 5, 2, 8, 4, 7, 1, 5, 1, 6, 8, 3, 6, 6, 5, 0, 1, 6, 0, 2, 7, 8, 7, 0, 4, 5, 0, 5, 9, 8, 3, 5, 7, 8, 0, 4, 0, 6, 2, 2, 4, 0, 5, 4, 5, 6, 5, 0, 5, 8, 3, 7, 5, 9, 8, 1, 0, 0, 3, 4, 5, 1, 2

Offset

1,3

Comments

Let a be an integer and let p be a prime of the form a^2 + 3*a + 9 (see A005471). Shanks introduced a family of cyclic cubic fields generated by the roots of the polynomial x^3 - a*x^2 - (a + 3)*x - 1. The polynomial has three real roots, one positive and two negative.

In the case a = 4, corresponding to the prime p = 37, the three real roots of the cubic x^3 - 4*x^2 - 7*x - 1 in descending order are r_0 = 5.3447123654..., r_1 = - 0.1576115578... and r_2 = - 1.1871008076....

Here we consider the absolute value of the root r_2. See A348726 (r_0) and A348727 (|r_1|) for the other two roots.

Links

Table of n, a(n) for n=1..100.

T. W. Cusick and Lowell Schoenfeld, A table of fundamental pairs of units in totally real cubic fields, Math. Comp. 48 (1987), 147-158 (see case 37 in the table)

D. Shanks, The simplest cubic fields, Math. Comp., 28 (1974), 1137-1152

Formula

|r_2| = 2*(-cos(Pi/37) + cos(6*Pi/37) + cos(8*Pi/37) + cos(10*Pi/37) - cos(11*Pi/37) + cos(14*Pi/37)) - 1.

|r_2| = |R(3)/R(1)|, where R(k) = sin(k*Pi/37)*sin(6*k*Pi/37)*sin(8*k*Pi/37)* sin(10*k*Pi/37)*sin(11*k*Pi/37)*sin(14*k*Pi/37).

Let R = <1, 6, 8, 10, 11, 14, 23, 26, 27, 29, 31, 36> denote the multiplicative subgroup of nonzero cubic residues in the finite field Z_37, with cosets 2*R = {2, 9, 12, 15, 16, 17, 20, 21, 22, 25, 28, 35} and 3*R = {3, 4, 5, 7, 13, 18, 19, 24, 30, 32, 33, 34}. Then the constant equals Product_{n >= 0} ( Product_{k in the coset 3*R} (37*n+k) )/( Product_{k in the group R} (37*n + k) ).

Example

1.18710080760640920168337009872276109935284715168366...

Maple

R := k -> sin(k*Pi/37)*sin(6*k*Pi/37)*sin(8*k*Pi/37)*sin(10*k*Pi/37)* sin(11*k*Pi/37)*sin(14*k*Pi/37): evalf(-R(3)/R(1), 100);

Mathematica

f[ks_, m_] := Product[Sin[k*Pi/m], {k, ks}]; ks = {1, 6, 8, 10, 11, 14}; RealDigits[f[3*ks, 37]/f[ks, 37], 10, 100][[1]] (* Amiram Eldar, Nov 08 2021 *)

Crossrefs

Cf. A005471, A160389, A255240, A255241, A255249, A348720 - A348729.

Sequence in context: A261303 A259348 A257238 * A255702 A154401 A248582

Adjacent sequences: A348725 A348726 A348727 * A348729 A348730 A348731

Keyword

nonn,cons,easy

Author

Peter Bala, Oct 31 2021

Status

approved