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Narayana Cow Sequence


The Naraya cow sequence, named after the 14th-century Indian mathematician Narayana Pandita, considers a herd that begins with one cow in the first year and in which each cow gives birth to one calf a year from the age of three onwards. The sequence for years n=1, 2, ... then gives 1, 1, 1 + 1 cow born = 2, 2 + 1 cow born = 3, 3 + 1 cow born = 4, 4 + 2 cows born = 6, and so one. Continuing gives the sequence 1, 1, 2, 3, 4, 6, 9, 13, 19, 28, 41, 60, ... (OEIS A000930).

The nth Narayana cow number N_n gives the number of integer compositions of n involving only 1 and 3, the first few of which are shown in the following table.

nN_ncompositions of n using 1 and 3
111
211+1
323, 1+1+1
431+3, 3+1, 1+1+1+1
541+1+3, 1+3+1, 3+1+1, 1+1+1+1+1
663+3, 1+1+1+3, 1+1+3+1, 1+3+1+1, 3+1+1+1, 1+1+1+1+1+1

Based on its definition, the Naraya cow sequence is evidently related to both the Fibonacci sequene and Padovan sequence.

The terms of the sequence are given by the linear recurrence

 N_n=N_(n-1)+N_(n-3)
(1)

with N_1=1, N_2=1, and N_3=2. They have generating function

 f(x)=-(x^2+1)/(x^3+x-1).
(2)

They also have a closed form in terms of a generalized hypergeometric function

 N_n=_3F_2((1-n)/3,(2-n)/3,-n/3;(1-n)/2,-n/2;-(27)/4).
(3)

The limit of consecutive terms is the supergolden ratio

 lim_(n->)(N_n)/(N_(n-1))=psi.
(4)

See also

Supergolden Ratio, Narayana Number, Narayana Triangle

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References

Lin, X. "On the Recurrence Properties of Narayana's Cows Sequence." Symmetry 13, 1-12, 2021.Narayana Pandita. Ganita Kaumudi. 1356.Pegg, E. Jr. "Shattering the Plane with Twelve New Substitution Tilings Using 2, phi, psi, chi, rho." Mar. 7, 2019. https://blog.wolfram.com/2019/03/07/shattering-the-plane-with-twelve-new-substitution-tilings-using-2-phi-psi-chi-rho/.Sloane, N. J. A. Sequence A000930 in "The On-Line Encyclopedia of Integer Sequences."

Cite this as:

Weisstein, Eric W. "Narayana Cow Sequence." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/NarayanaCowSequence.html

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