OFFSET
1,2
COMMENTS
Consider the array of triangular, square and centered polygonal numbers (irregular variant of A086272 and A086273):
1 3 6 10 15 21 28 36 45 55 A000217
1 4 9 16 25 36 49 64 81 100 A000290
1 6 16 31 51 76 106 141 181 226 A005891
1 7 19 37 61 91 127 169 217 271 A003215
1 8 22 43 71 106 148 197 253 316 A069099
1 9 25 49 81 121 169 225 289 361 A016754
1 10 28 55 91 136 190 253 325 406 A060544
1 11 31 61 101 151 211 281 361 451 A062786
1 12 34 67 111 166 232 309 397 496 A069125
1 13 37 73 121 181 253 337 433 541 A003154
1 14 40 79 131 196 274 365 469 586 A069126
1 15 43 85 141 211 295 393 505 631 A069127
etc. The sequence contains the antidiagonal sums of this array. - R. J. Mathar, Jun 05 2011
For comparison, the antidiagonal sums of A086270 are essentially A006522 starting at the 4th term. - R. J. Mathar, Sep 20 2008
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).
FORMULA
a(n) = (n-1)*(n^3+11*n^2-38*n+120)/24, n>1. - R. J. Mathar, Sep 12 2008
G.f.: x*(1-x+x^2+x^3-x^5)/(1-x)^5. - Alexander R. Povolotsky, Jun 06 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Dan Graybill (clopen(AT)comcast.net), Aug 12 2008
STATUS
approved