A384624 Decimal expansion of the volume of a pentagonal orthobicupola with unit edge.

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

Offset: 1

Author

Paolo Xausa, Jun 05 2025

Keywords

• nonn
• cons
• easy

Comments

The pentagonal orthobicupola is Johnson solid J_30.

Also the volume of a pentagonal gyrobicupola (Johnson solid J_31) with unit edge.

Examples

			4.6480906366663862618788982249750349805874911461487...
		

Links

• Paolo Xausa, Table of n, a(n) for n = 1..10000
• Wikipedia, Pentagonal orthobicupola.
• Wikipedia, Pentagonal gyrobicupola.

Crossrefs

Cf. A384625 (surface area).

Cf. A010532, A384287.

Programs

Mathematica

First[RealDigits[(5 + Sqrt[80])/3, 10, 100]] (* or *)
First[RealDigits[PolyhedronData["J30", "Volume"], 10, 100]]

Formula

Equals (5 + 4*sqrt(5))/3 = (5 + A010532)/3.

Equals the largest root of 9*x^2 - 30*x - 55.