A331250 -id:A331250 - cp's OEIS frontend

A010466 Decimal expansion of square root of 8.

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

Offset: 1

N. J. A. Sloane

Sqrt(8) = 2*sqrt(2) is the length of the longest (rigid) ladder that can be carried horizontally around a right angled corner in a hallway of unit width. - Lekraj Beedassy, Apr 19 2006
Continued fraction expansion is 2 followed by {1, 4} repeated. - Harry J. Smith, Jun 05 2009
This is the second Lagrange number. - Alonso del Arte, Dec 06 2011
Also 2*sqrt(2) is the ratio of the perimeter of a square to its diameter (diagonal length). - Rick L. Shepherd, Dec 29 2016
Uchiyama shows that every interval (n, n + c*n^(1/4)) contains an integer that is the sum of two squares, where c = 2^(3/2). - Michel Marcus, Jan 03 2018
This is the area of the eighth-smallest triangle with integer side lengths (2, 3, 3), or the seventh-smallest triangle if two smaller triangles with the same area are counted only once (see A331251). - Hugo Pfoertner, Feb 12 2020
Diameter of a sphere whose surface area equals 8*Pi. More generally, the square root of x is also the diameter of a sphere whose surface area equals x*Pi. - Omar E. Pol, Feb 13 2020
Sqrt(8) = area between the curves y = sin(x) and y = cos(x) for Pi/4 < x < 5 Pi/4; this is one of infinitely many congruent convex regions bounded by the two curves. - Clark Kimberling, May 03 2020
Area of the regular 8-gon with circumradius =1. - R. J. Mathar, Aug 24 2023

			2.828427124746190097603377448419396157139343750753896146353359475981464...
Sqrt(8) = sqrt(1+2*i*sqrt(2)) + sqrt(1-2*i*sqrt(2)) = sqrt(1/2+2*i*sqrt(3)) + sqrt(1/2-2*i*sqrt(3)), where i=sqrt(-1). - _Bruno Berselli_, Nov 20 2012
1 + 3/4 + 3*5/(4*8) + 3*5*7/(4*8*12) + 3*5*7*9/(4*8*12*16) + ... - _Bruno Berselli_, Mar 16 2014

John H. Conway and Richard K. Guy, The Book of Numbers, New York: Springer-Verlag, 1996. See p. 187.
S. R. Finch, Moving Sofa Constant, Sect. 8.12 in Mathematical Constants. Cambridge, England: Cambridge University Press, pp. 519-523, 2003.

Harry J. Smith, Table of n, a(n) for n = 1..20000
Jason Kimberley, Index of expansions of sqrt(d) in base b
R. J. Nemiroff & J. Bonnell, The first 1 million digits of the square root of 8
R. J. Nemiroff & J. Bonnell, Plouffe's Inverter, The first 1 million digits of the square root of 8
Ana Rechtman, Juin 2023, 3e défi, Images des Mathématiques, CNRS, 2023.
S. Uchiyama, On the distribution of integers representable as a sum of two h-th powers, J. Fac. Sci. Hokkaido Univ. Ser. I, 18, 124-127, 1964/1965.
Eric Weisstein's World of Mathematics, Moving Ladder Problem
Index entries for algebraic numbers, degree 2

Cf. A040005 (continued fraction).

Cf. A331250, A331251.

SetDefaultRealField(RealField(100)); Sqrt(8); // Vincenzo Librandi, Feb 13 2020

evalf(2^(3/2)) ; # R. J. Mathar, Jul 15 2013

RealDigits[N[Sqrt[8],200]][[1]] (* Vladimir Joseph Stephan Orlovsky, Mar 04 2011 *)

default(realprecision, 20080); x=sqrt(8); for (n=1, 20000, d=floor(x); x=(x-d)*10; write("b010466.txt", n, " ", d));  \\ Harry J. Smith, Jun 02 2009

Equals 1 + Sum_{n>=1} ( Product_{k=1..n} (2k+1)/(4k) ). - Bruno Berselli, Mar 16 2014
Equals 2*A002193. - R. J. Mathar, Jan 14 2021
From Peter Bala, Mar 01 2022: (Start)
Equals 3*Sum_{n >= 0} (1/(4*n+1) - 1/(4*n-3))*binomial(1/2,n). Cf. A002580 and A175576.
Equals 4*hypergeom([-1/2, -3/4], [5/4], -1). (End)
Equals 8 * A020765. - R. J. Mathar, Aug 24 2023

A140239 Decimal expansion of 3*sqrt(15)/4.

Original entry on oeis.org

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

Offset: 1

Rick L. Shepherd, May 14 2008

Area of the obtuse scalene triangle with sides of lengths 2, 3 and 4, the scalene triangle with least integer side lengths.

This is the area of the ninth-smallest triangle with integer side lengths, or the eighth-smallest triangle if two smaller triangles with the same area are counted only once (see A331251). - Hugo Pfoertner, Feb 12 2020

			2.90473750965556266388444904983679970812469127896869311994068032458511231895...

Daniel Starodubtsev, Table of n, a(n) for n = 1..10000
Index entries for algebraic numbers, degree 2

Cf. A140240, A140241, A140242, A140243, A140244, A140245, A140246, A140247, A140248, A140249, A088543, A010472, A331250, A331251.

RealDigits[(3Sqrt[15])/4,10,120][[1]] (* Harvey P. Dale, Apr 03 2013 *)

3*sqrt(15)/4 = 3*A010472/4.

A135622 16*Area^2 of integer triangles [A070080(n),A070081(n),A070082(n)].

Original entry on oeis.org

3, 15, 48, 35, 63, 128, 63, 135, 243, 240, 320, 99, 231, 275, 495, 384, 576, 768, 143, 351, 455, 819, 975, 560, 896, 1008, 1344, 195, 495, 675, 1215, 735, 1575, 1875, 768, 1280, 1536, 2048, 2304, 255, 663, 935, 1683, 1071, 2295, 2499, 2975, 1008, 1728

Offset: 1

Franz Vrabec, Feb 29 2008

			A070080(4)=1, A070081(4)=3, A070082(4)=3, so a(4)=(1+3+3)*(-1+3+3)*(1-3+3)*(1+3-3)=35.

See the formula section for the relationships with A070080, A070081, A070082, A070086.
Cf. A317182 (range of values), A331011 (nonunique values), A331250 (counts triangles by area).
Cf. A316853 (with terms ordered as for A316841), and using this order for other sets of triangles: A046131, A055595, A070786.

a(n)=(u+v+w)*(-u+v+w)*(u-v+w)*(u+v-w), where u=A070080(n), v=A070081(n), w=A070082(n).

A070086(n) = round(sqrt(a(n))/4).

A381100 Number of integer triples i <= j <= k such that a non-degenerate triangle with sides (i, j, k) fits inside an equilateral triangle with sides (n, n, n), possibly touching its boundary from inside.

Original entry on oeis.org

1, 2, 5, 10, 18, 29, 44, 62, 82, 109, 141, 180, 226, 279, 339, 403, 475, 557, 651, 755, 870, 993, 1125, 1269, 1425, 1595, 1780, 1976, 2188, 2417, 2652, 2905, 3173, 3461, 3769, 4090, 4436, 4788, 5161, 5558, 5968, 6405, 6857, 7340, 7840, 8355, 8893, 9463, 10048

Offset: 1

Vladimir Reshetnikov, Feb 13 2025

			For n = 2, triangles (1, 1, 1) and (2, 2, 2) can fit inside (2, 2, 2), so a(2) = 2.

K. A. Post, Triangle in a triangle: On a problem of Steinhaus. Geom Dedicata 45, 115-120 (1993).

Cf. A331250.

ClearAll[checkOnce, triangleInTriangleQ, a];
checkOnce[{a_, b_, c_}, {p_, q_, r_}] := With[{d = (a + b - c) (a - b + c) (-a + b + c) (a + b + c), s = (p + q - r) (p - q + r) (-p + q + r) (p + q + r), u = p^2 + q^2 - r^2, v = p^2 - q^2 + r^2}, p <= a && a^2 s <= d p^2 && u v >= 0 && s (a^2 - b^2 + c^2)^2 <= d (2 a p - u)^2 && s (a^2 + b^2 - c^2)^2 <= d (2 a p - v)^2];
triangleInTriangleQ[a_, b_, c_, p_, q_, r_] := Or @@ Flatten[Table[checkOnce[abc, pqr], {abc, {{a, b, c}, {b, c, a}, {c, a, b}}}, {pqr, Permutations[{p, q, r}]}]];
a[n_] := Total[Flatten[Table[Boole[triangleInTriangleQ[n, n, n, p, q, r]], {p, n}, {q, p}, {r, p - q + 1, q}]]];
Table[a[n], {n, 1, 49}]

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A010466 Decimal expansion of square root of 8.

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A140239 Decimal expansion of 3*sqrt(15)/4.

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A135622 16*Area^2 of integer triangles [A070080(n),A070081(n),A070082(n)].

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A381100 Number of integer triples i <= j <= k such that a non-degenerate triangle with sides (i, j, k) fits inside an equilateral triangle with sides (n, n, n), possibly touching its boundary from inside.

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