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A055426 Number of points in Z^n of norm <= 2. 2
1, 5, 13, 33, 89, 221, 485, 953, 1713, 2869, 4541, 6865, 9993, 14093, 19349, 25961, 34145, 44133, 56173, 70529, 87481, 107325, 130373, 156953, 187409, 222101, 261405, 305713, 355433, 410989, 472821, 541385, 617153, 700613, 792269, 892641 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
LINKS
FORMULA
a(n) = (3+2*n+16*n^2-8*n^3+2*n^4)/3. - corrected by Colin Barker, Jul 07 2013
G.f.: -(x+1)*(9*x^3-x^2-x+1) / (x-1)^5. - Colin Barker, Jul 07 2013
a(0)=1, a(1)=5, a(2)=13, a(3)=33, a(4)=89, a(n)=5*a(n-1)-10*a(n-2)+ 10*a(n-3)- 5*a(n-4)+a(n-5). - Harvey P. Dale, Feb 09 2015
MATHEMATICA
LinearRecurrence[{5, -10, 10, -5, 1}, {1, 5, 13, 33, 89}, 40] (* Harvey P. Dale, Feb 09 2015 *)
CROSSREFS
Row n=2 of A302997.
Sequence in context: A027051 A109786 A283959 * A146621 A147086 A032406
KEYWORD
nonn,easy
AUTHOR
STATUS
approved

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Last modified July 15 23:38 EDT 2024. Contains 374343 sequences. (Running on oeis4.)