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.

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A040380 Continued fraction for sqrt(401).

Original entry on oeis.org

20, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40
Offset: 0

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Examples

			20 + 1/(40 + 1/(40 + 1/(40 + 1/(40 + ...)))) = sqrt(401).
		

Crossrefs

Cf. A041760/A041761 (convergents).

Programs

  • Maple
    with(numtheory): Digits := 300: convert(evalf(sqrt(401)),confrac);

Formula

From Elmo R. Oliveira, Feb 15 2024: (Start)
a(n) = 40 for n >= 1.
G.f.: 20*(1+x)/(1-x).
E.g.f.: 40*exp(x) - 20.
a(n) = 20*A040000(n) = 10*A040002(n) = 5*A040012(n). (End)

A041760 Numerators of continued fraction convergents to sqrt(401).

Original entry on oeis.org

20, 801, 32060, 1283201, 51360100, 2055687201, 82278848140, 3293209612801, 131810663360180, 5275719744020001, 211160600424160220, 8451699736710428801, 338279150068841312260, 13539617702490362919201, 541922987249683358080300
Offset: 0

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Crossrefs

Programs

  • Mathematica
    Numerator[Convergents[Sqrt[401], 30]] (* Vincenzo Librandi, Nov 07 2013 *)

Formula

a(n) = 40*a(n-1)+a(n-2) for n>1, a(0)=20, a(1)=801. G.f.: (20+x)/(1-40*x-x^2). [Philippe Deléham, Nov 23 2008]
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