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A022267 a(n) = n*(9*n + 1)/2. 16
0, 5, 19, 42, 74, 115, 165, 224, 292, 369, 455, 550, 654, 767, 889, 1020, 1160, 1309, 1467, 1634, 1810, 1995, 2189, 2392, 2604, 2825, 3055, 3294, 3542, 3799, 4065, 4340, 4624, 4917, 5219, 5530, 5850, 6179 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

From Floor van Lamoen, Jul 21 2001: (Start)

Write 0, 1, 2, 3, 4, ... in a triangular spiral; then a(n) is the sequence found by reading the line from 0 in the direction 0, 5, ... . The spiral begins:

.

            15

            / \

          16  14

          /     \

        17   3  13

        /   / \   \

      18   4   2  12

      /   /     \   \

    19   5   0---1  11

    /   /             \

  20   6---7---8---9--10

.

(End)

LINKS

Lei Zhou, Table of n, a(n) for n = 0..10000

Milan Janjic, Two Enumerative Functions

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

a(n) = A110449(n, 4) for n>3.

From Bruno Berselli, Feb 11 2011: (Start)

G.f.: x*(5 + 4*x)/(1 - x)^3.

a(n) = 4*A000217(n) + A000566(n). (End)

a(n) = 9*n + a(n-1) - 4 with n>0, a(0)=0. - Vincenzo Librandi, Aug 04 2010

a(n) = A218470(9*n+4). - Philippe Deléham, Mar 27 2013

a(n) = A000217(5*n) - A000217(4*n). - Bruno Berselli, Oct 13 2016

E.g.f.: (1/2)*(9*x^2 + 10*x)*exp(x). - G. C. Greubel, Jul 17 2017

MAPLE

seq(binomial(9*n+1, 2)/9, n=0..37); # Zerinvary Lajos, Jan 21 2007

MATHEMATICA

Table[ n (9 n + 1)/2, {n, 0, 40}] (* or *) LinearRecurrence[{3, -3, 1}, {0, 5, 19}, 40] (* Harvey P. Dale, Jul 01 2013 *)

PROG

(PARI) vector(100, n, (n-1)*(9*n-8)/2) \\ Derek Orr, Feb 06 2015

CROSSREFS

Cf. A000217, A051682, A110449, A235332.

Cf. numbers of the form n*(d*n+10-d)/2: A008587, A056000, A028347, A140090, A014106, A028895, A045944, A186029, A007742, A033429, A022268, A049452, A186030, A135703, A152734, A139273.

Cf. similar sequences listed in A254963.

Cf. similar sequences listed in A022289.

Sequence in context: A234801 A089148 A098319 * A094465 A020580 A172043

Adjacent sequences:  A022264 A022265 A022266 * A022268 A022269 A022270

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified December 13 03:41 EST 2019. Contains 329968 sequences. (Running on oeis4.)