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A300522

a(n) = (5*n + 3)*(5*n + 4)*(5*n + 5)/6.

10, 120, 455, 1140, 2300, 4060, 6545, 9880, 14190, 19600, 26235, 34220, 43680, 54740, 67525, 82160, 98770, 117480, 138415, 161700, 187460, 215820, 246905, 280840, 317750, 357760, 400995, 447580, 497640, 551300, 608685, 669920, 735130, 804440, 877975, 955860, 1038220, 1125180

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OFFSET

0,1

COMMENTS

Al-Saedi has discovered that p(10*n+2,4) + p(10*n+3,4) + p(10*n+4,4) == 0 (mod 5), where p(m,k) denote the number of partitions of m into at most k parts [see Theorem 3.6, formula 24, in Links and References sections].

Hirschhorn showed that p(10*n+2,4) + p(10*n+3,4) + p(10*n+4,4) = (5*n+3)*(5*n+4)*(5*n+5)/6 [see References section: paragraph 3, "Proofs of (1.5)-(1.8)"].

The sequence binomial(5*m,3), m>=0, begins 0, 0, 0, 10, 120, 455, 1140, 2300, 4060, ... - N. J. A. Sloane, Jun 13 2020

REFERENCES

Ali H. Al-Saedi, Using Periodicity to Obtain Partition Congruences, Journal of Number Theory, Vol. 178, 2017, pages 158-178.

Michael D. Hirschhorn, Congruences modulo 5 for partitions into at most four parts, The Fibonacci Quarterly, Vol. 56, Number 1, 2018, pages 34-37.

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Ali H. Al-Saedi, Using Periodicity to Obtain Partition Congruences, arXiv:1609.03633 [math.NT], 2017, pages 12-13.

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

FORMULA

O.g.f.: 5*(2 + 16*x + 7*x^2)/(1 - x)^4 [formula 4.1 in Hirschhorn's paper].

E.g.f.: 5*(12 + 132*x + 135*x^2 + 25*x^3)*exp(x)/6.

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4).