cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A319015 Decimal expansion of Sum_{k>=0} 1/2^(k^2).

Original entry on oeis.org

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

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Author

Ilya Gutkovskiy, Sep 07 2018

Keywords

Comments

The binary expansion is the characteristic function of the squares (A010052).
This constant is transcendental (Nesterenko, 1996). - Amiram Eldar, Apr 30 2020

Examples

			1.5644684136059385793347... = (1.1001000010000001000000001...)_2.
                               | |  |    |      |        |
                               0 1  4    9     16       25
		

Crossrefs

Programs

  • Mathematica
    RealDigits[(1 + EllipticTheta[3, 0, 1/2])/2, 10, 110] [[1]]
  • PARI
    suminf(k=0, 1/2^(k^2)) \\ Michel Marcus, Sep 08 2018

Formula

Equals (1 + theta_3(1/2))/2, where theta_3 is the Jacobi theta function.
Equals 1 + Sum_{k>=1} lambda(k)/(2^k - 1), where lambda is the Liouville function (A008836). - Amiram Eldar, Apr 30 2020
Equals 1 + Sum_{k>=1} floor(sqrt(k))/2^(k+1) (Shamos, 2011, p. 4). - Amiram Eldar, Mar 12 2024