A176324 -id:A176324 - cp's OEIS frontend

A010720 Period 2: repeat (5,9).

5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5, 9, 5

Offset: 0

N. J. A. Sloane

Continued fraction expansion of A176324. - R. J. Mathar, Mar 08 2012

Index entries for linear recurrences with constant coefficients, signature (0,1).

Table[5 + 4 Mod[n, 2], {n, 0, 50}] (* Jinyuan Wang, Feb 26 2020 *)

a(n)=n%2*4+5 \\ Charles R Greathouse IV, Jul 13 2016

a(n) = -2*(-1)^n + 7. - Paolo P. Lava, Oct 20 2006

a(n) = a(n-2) for n > 1; a(0) = 5, a(1) = 9. G.f.: (5+9*x)/((1-x)*(1+x)). - Vincenzo Librandi, Aug 01 2010

A386754 Decimal expansion of the surface area of a triangular hebesphenorotunda with unit edges.

Original entry on oeis.org

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

Offset: 2

Paolo Xausa, Aug 01 2025

The triangular hebesphenorotunda is Johnson solid J_92.

			16.3886735377190679125324060543187225412004474656...

Paolo Xausa, Table of n, a(n) for n = 2..10000
Wikipedia, Triangular hebesphenorotunda.

Cf. A176324 (volume).

Cf. A002194, A010476.

First[RealDigits[(12 + 19*A002194 + 3*Sqrt[5*(5 + A010476)])/4, 10, 100]] (* or *)
First[RealDigits[PolyhedronData["J92", "SurfaceArea"], 10, 100]]

Equals (12 + 19*sqrt(3) + 3*sqrt(5*(5 + 2*sqrt(5))))/4 = (12 + 19*A002194 + 3*sqrt(5*(5 + A010476)))/4.

Equals the largest root of 256*x^8 - 6144*x^7 - 19200*x^6 + 1119744*x^5 - 1614816*x^4 - 57096576*x^3 + 76850100*x^2 + 856278216*x + 56001861.

cp's OEIS Frontend

A010720 Period 2: repeat (5,9).

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