A010476 Decimal expansion of square root of 20.

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

Offset

1,1

Comments

Continued fraction expansion is 4 followed by {2, 8} repeated. - Harry J. Smith, Jun 03 2009

Links

Harry J. Smith, Table of n, a(n) for n = 1..20000

Index entries for algebraic numbers, degree 2

Formula

sqrt(20) = 2*sqrt(5). - Alonso del Arte, Jun 26 2015

Equals Sum_{k>=0} binomial(2*k,k) * k/5^k. - Amiram Eldar, Aug 03 2020

Example

4.472135954999579392818347337462552470881236719223051448541794490821041....

Mathematica

RealDigits[N[Sqrt[20], 100]][[1]] (* Vladimir Joseph Stephan Orlovsky, Feb 21 2011 *)

Prog

(PARI)  default(realprecision, 20080); x=sqrt(20); for (n=1, 20000, d=floor(x); x=(x-d)*10; write("b010476.txt", n, " ", d));  \\ Harry J. Smith, Jun 03 2009

Crossrefs

Except for offset, same as A020762.

Cf. A040015 (continued fraction). - Harry J. Smith, Jun 03 2009

Cf. A002163 (decimal expansion of square root of 5).

Sequence in context: A021695 A131844 A344212 * A020762 A204158 A053510

Adjacent sequences: A010473 A010474 A010475 * A010477 A010478 A010479

Keyword

nonn,cons,easy

Author

N. J. A. Sloane

Status

approved