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A067705
a(n) = 11*n^2 + 22*n.
3
33, 88, 165, 264, 385, 528, 693, 880, 1089, 1320, 1573, 1848, 2145, 2464, 2805, 3168, 3553, 3960, 4389, 4840, 5313, 5808, 6325, 6864, 7425, 8008, 8613, 9240, 9889, 10560, 11253, 11968, 12705, 13464, 14245, 15048, 15873, 16720, 17589, 18480
OFFSET
1,1
COMMENTS
Numbers k such that 11*(11 + k) is a perfect square.
FORMULA
G.f.: 11*x*(3-x)/(1-x)^3. - Vincenzo Librandi, Jul 07 2012
a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). - Vincenzo Librandi, Jul 07 2012
MATHEMATICA
Select[ Range[20000], IntegerQ[ Sqrt[ 11(11 + # )]] & ]
CoefficientList[Series[11 (3 - x)/(1 - x)^3, {x, 0, 50}], x] (* Vincenzo Librandi, Jul 07 2012 *)
PROG
(PARI) a(n)=11*n*(n+2) \\ Charles R Greathouse IV, Dec 07 2011
(Magma) [11*n*(n+2): n in [1..50]]; // Vincenzo Librandi, Jul 07 2012
CROSSREFS
Cf. A067724, A067725, A067726, A067727, A067728 (if 11 is replaced by 3, 5, 6, 7, 8 respectively), A067707 (12).
Sequence in context: A080700 A292366 A080200 * A075213 A231392 A231460
KEYWORD
nonn,easy
AUTHOR
Robert G. Wilson v, Feb 05 2002
STATUS
approved