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A163761
a(n) = 10*n*(n+1).
3
0, 20, 60, 120, 200, 300, 420, 560, 720, 900, 1100, 1320, 1560, 1820, 2100, 2400, 2720, 3060, 3420, 3800, 4200, 4620, 5060, 5520, 6000, 6500, 7020, 7560, 8120, 8700, 9300, 9920, 10560, 11220, 11900, 12600, 13320, 14060, 14820, 15600, 16400, 17220, 18060, 18920
OFFSET
0,2
COMMENTS
20 times the n-th triangular number.
a(n) is the number of one-sided n-step prudent walks, from (0,0) to (3,3), for n-6 is even. - Shanzhen Gao, Apr 26 2011
Numbers k such that 10*k + 25 is a square. - Bruno Berselli, May 14 2018
LINKS
Shanzhen Gao and Keh-Hsun Chen, Tackling Sequences From Prudent Self-Avoiding Walks, FCS'14, The 2014 International Conference on Foundations of Computer Science.
Shanzhen Gao and H. Niederhausen, Sequences Arising From Prudent Self-Avoiding Walks, (submitted to INTEGERS: The Electronic Journal of Combinatorial Number Theory).
FORMULA
a(n) = 20*A000217(n) = 10*A002378(n).
G.f.: 20*x/(1-x)^3.
E.g.f.: 10*x*(x+2)*exp(x). - G. C. Greubel, Aug 03 2017
From Amiram Eldar, Feb 22 2023: (Start)
Sum_{n>=1} 1/a(n) = 1/10.
Sum_{n>=1} (-1)^(n+1)/a(n) = (2*log(2) - 1)/10.
Product_{n>=1} (1 - 1/a(n)) = -(10/Pi)*cos(sqrt(7/5)*Pi/2).
Product_{n>=1} (1 + 1/a(n)) = (10/Pi)*cos(sqrt(3/5)*Pi/2). (End)
MATHEMATICA
LinearRecurrence[{3, -3, 1}, {0, 20, 60}, 50] (* or *) Table[10*n*(n+1), {n, 0, 50}] (* G. C. Greubel, Aug 03 2017 *)
PROG
(Magma) [10*n*(n+1): n in [0..50]];
(PARI) a(n)=10*n*(n+1) \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
Sequence in context: A220046 A275167 A344200 * A154072 A078184 A362268
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Aug 03 2009
EXTENSIONS
Entries checked by R. J. Mathar, Aug 06 2009
STATUS
approved