A375152 Decimal expansion of the apothem (inradius) of a regular 9-gon with unit side length.

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

Offset

1,2

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Regular Polygon.

Wikipedia, Apothem.

Index entries for algebraic numbers, degree 6.

Formula

Equals cot(Pi/9)/2 = A019968/2.

Equals 1/(2*tan(Pi/9)) = 1/(2*A019918).

Equals A375151*cos(Pi/9) = A375151*A019879.

Equals A375151 - A375153.

Largest of the 6 real-valued roots of 192*x^6 -432*x^4 +132*x^2 -1=0. - R. J. Mathar, Aug 29 2025

Example

1.3737387097273111393808320132488363588759362995854...

Mathematica

First[RealDigits[Cot[Pi/9]/2, 10, 100]]

Prog

(PARI) .5/tan(Pi/9) \\ Charles R Greathouse IV, Feb 05 2025

Crossrefs

Cf. A375151 (circumradius), A375153 (sagitta), A256853 (area).

Cf. apothem of other polygons with unit side length: A020769 (triangle), A020761 (square), A375067 (pentagon), A010527 (hexagon), A374971 (heptagon), A174968 (octagon), A179452 (10-gon), A375191 (11-gon), A375193 (12-gon).

Cf. A019879, A019918, A019968.

Sequence in context: A161973 A010705 A244189 * A200481 A016665 A320831

Adjacent sequences: A375149 A375150 A375151 * A375153 A375154 A375155

Keyword

nonn,cons,easy

Author

Paolo Xausa, Aug 01 2024

Status

approved