A384140 Decimal expansion of the volume of an elongated pentagonal bipyramid with unit edge.

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

Offset: 1

Author

Paolo Xausa, May 20 2025

Keywords

• nonn
• cons
• easy

Comments

The elongated pentagonal bipyramid is Johnson solid J_16.

Examples

			2.32348306538061606412644311644954928569409236664...
		

Links

• Paolo Xausa, Table of n, a(n) for n = 1..10000
• Wikipedia, Elongated pentagonal bipyramid.

Crossrefs

Cf. A384141 (surface area).

Cf. A002163, A383852, A384138, A384139.

Programs

Mathematica

First[RealDigits[(5 + Sqrt[5] + 3*Sqrt[25 + 10*Sqrt[5]])/12, 10, 100]] (* or *)
First[RealDigits[PolyhedronData["J16", "Volume"], 10, 100]]

Formula

Equals (5 + sqrt(5) + 3*sqrt(25 + 10*sqrt(5)))/12 = (5 + A002163 + 3*sqrt(25 + 10*A002163))/12.

Equals the largest root of 20736*x^4 - 34560*x^3 - 44640*x^2 + 27600*x + 6025.