A375189 - OEIS

A375189

Decimal expansion of the sagitta of a regular 10-gon with unit side length.

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

(list; constant; graph; refs; listen; history; text; internal format)

OFFSET

-1,1

LINKS

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

Eric Weisstein's World of Mathematics, Regular Polygon.

Eric Weisstein's World of Mathematics, Sagitta.

Index entries for algebraic numbers, degree 4.

FORMULA

Equals tan(Pi/20)/2 = A019907/2.

Equals (1 + sqrt(5) - sqrt(5 + 2*sqrt(5)))/2.

Equals A001622 - A179452.

Minimal polynomial: 16*x^4 - 32*x^3 - 56*x^2 - 8*x + 1. - Amiram Eldar, May 14 2026

EXAMPLE

0.0791922201622681469194415463471832057169581080...

MATHEMATICA

First[RealDigits[Tan[Pi/20]/2, 10, 100]]

PROG

(PARI) tan(Pi/20)/2 \\ Charles R Greathouse IV, Feb 05 2025

CROSSREFS

Cf. A001622 (circumradius), A179452 (apothem), A178816 (area).

Cf. sagitta of other polygons with unit side length: A020769 (triangle), A174968 (square), A375068 (pentagon), A375069 (hexagon), A374972 (heptagon), A375070 (octagon), A256853 (9-gon), A375192 (11-gon), A375194 (12-gon).

Cf. A019907.

Sequence in context: A132806 A016629 A154203 * A055676 A296500 A202323

Adjacent sequences: A375186 A375187 A375188 * A375190 A375191 A375192

KEYWORD

nonn,cons,easy,changed

AUTHOR

Paolo Xausa, Aug 04 2024

STATUS

approved