A054776 -id:A054776 - cp's OEIS frontend

A006566 Dodecahedral numbers: a(n) = n(3n - 1)(3n - 2)/2.

0, 1, 20, 84, 220, 455, 816, 1330, 2024, 2925, 4060, 5456, 7140, 9139, 11480, 14190, 17296, 20825, 24804, 29260, 34220, 39711, 45760, 52394, 59640, 67525, 76076, 85320, 95284, 105995, 117480, 129766, 142880, 156849, 171700, 187460, 204156

Offset: 0

N. J. A. Sloane

Schlaefli symbol for this polyhedron: {5,3}.
A093485 = first differences; A124388 = second differences; third differences = 27. - Reinhard Zumkeller, Oct 30 2006
One of the 5 Platonic polyhedral (tetrahedral, cube, octahedral, dodecahedral and icosahedral) numbers (cf. A053012). - Daniel Forgues, May 14 2010
From Peter Bala, Sep 09 2013: (Start)
a(n) = binomial(3*n,3). Two related sequences are binomial(3*n+1,3) (A228887) and binomial(3*n+2,3) (A228888). The o.g.f.'s for these three sequences are rational functions whose numerator polynomials are obtained from the fourth row [1, 4, 10, 16, 19, 16, 10, 4, 1] of the triangle of trinomial coefficients A027907 by taking every third term:
Sum_{n >= 1} binomial(3*n,3)*x^n = (x + 16*x^2 + 10*x^3)/(1-x)^4;
Sum_{n >= 1} binomial(3*n+1,3)*x^n = (4*x + 19*x^2 + 4*x^3)/(1-x)^4;
Sum_{n >= 1} binomial(3*n+2,3)*x^n = (10*x + 16*x^2 + x^3)/(1-x)^4. (End)

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..1000
Tanya Khovanova, Recursive Sequences.
Hyun Kwang Kim, On Regular Polytope Numbers, Proc. Amer. Math. Soc., 131 (2002), 65-75.
Victor Meally, Letter to N. J. A. Sloane, no date.
Ed Pegg Jr, Dodecahedral 2024.
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992.
Franck Ramaharo, Statistics on some classes of knot shadows, arXiv:1802.07701 [math.CO], 2018.
Franck Ramaharo, A generating polynomial for the pretzel knot, arXiv:1805.10680 [math.CO], 2018.
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

Cf. A027907, A035006, A060544, A093485, A124388, A228887, A228888, A295421.

Cf. A000292 (tetrahedral numbers), A000578 (cubes), A005900 (octahedral numbers), A006564 (icosahedral numbers).

a006566 n = n * (3 * n - 1) * (3 * n - 2) `div` 2
a006566_list = scanl (+) 0 a093485_list  -- Reinhard Zumkeller, Jun 16 2013

[n*(3*n-1)*(3*n-2)/2: n in [0..40]]; // Vincenzo Librandi, Dec 11 2015

A006566:=(1+16*z+10*z**2)/(z-1)**4; # conjectured by Simon Plouffe in his 1992 dissertation

Table[n(3n-1)(3n-2)/2,{n,0,100}] (* Vladimir Joseph Stephan Orlovsky, Apr 13 2011 *)
LinearRecurrence[{4,-6,4,-1},{0,1,20,84},40] (* Harvey P. Dale, Jul 24 2013 *)
CoefficientList[Series[x (1 + 16 x + 10 x^2)/(1 - x)^4, {x, 0, 40}], x] (* Vincenzo Librandi, Dec 11 2015 *)

PARI
```
a(n)=n*(3*n-1)*(3*n-2)/2
```

G.f.: x(1 + 16x + 10x^2)/(1 - x)^4.
a(n) = A000292(3n-3) = A054776(n)/6 = n*A060544(n).
a(n) = C(n+2,3) + 16 C(n+1,3) + 10 C(n,3).
a(0)=0, a(1)=1, a(2)=20, a(3)=84, a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). - Harvey P. Dale, Jul 24 2013
a(n) = binomial(3*n,3). a(-n) = - A228888(n). Sum_{n>=1} 1/a(n) = 1/2*( sqrt(3)*Pi - 3*log(3) ). Sum_{n>=1} (-1)^n/a(n) = 1/3*sqrt(3)*Pi - 4*log(2). - Peter Bala, Sep 09 2013
a(n) = A006564(n) + A035006(n). - Peter M. Chema, May 04 2016
E.g.f.: x*(2 + 18*x + 9*x^2)*exp(x)/2. - Ilya Gutkovskiy, May 04 2016
From Amiram Eldar, Jan 09 2024: (Start)
Sum_{n>=1} 1/a(n) = (sqrt(3)*Pi - 3*log(3))/2 (A295421).
Sum_{n>=1} (-1)^(n+1)/a(n) = (12*log(2) - sqrt(3)*Pi)/3. (End)

More terms from Henry Bottomley, Nov 23 2001

A268685 a(n) = 3(n + 1)(n + 2)(3n + 1)(3n + 4)/4.

Original entry on oeis.org

6, 126, 630, 1950, 4680, 9576, 17556, 29700, 47250, 71610, 104346, 147186, 202020, 270900, 356040, 459816, 584766, 733590, 909150, 1114470, 1352736, 1627296, 1941660, 2299500, 2704650, 3161106, 3673026, 4244730, 4880700, 5585580, 6364176, 7221456, 8162550

Offset: 0

Ilya Gutkovskiy, Feb 11 2016

a(n) is the total volume of the family of (n+1) rectangular prisms, where the k-th prism has dimensions (3k) X (3k-1) X (3k-2). - Wesley Ivan Hurt, Oct 02 2018

			a(0) = 1*2*3 = 6;
a(1) = 1*2*3 + 4*5*6 = 126;
a(2) = 1*2*3 + 4*5*6 + 7*8*9 = 630;
a(3) = 1*2*3 + 4*5*6 + 7*8*9 + 10*11*12 = 1950;
a(4) = 1*2*3 + 4*5*6 + 7*8*9 + 10*11*12 + 13*14*15 = 4680;
a(5) = 1*2*3 + 4*5*6 + 7*8*9 + 10*11*12 + 13*14*15 + 16*17*18 = 9576, etc.

Felix Fröhlich, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

Cf. A000027, A054776, A116689, A135036.

Trisection of A319014 and A319867.

[3*(n + 1)*(n + 2)*(3*n + 1)*(3*n + 4)/4: n in [0..40]]; // Vincenzo Librandi, Feb 11 2016

Table[3 (n + 1) (n + 2) (3 n + 1) ((3 n + 4)/4), {n, 0, 32}] (* or *) LinearRecurrence[{5, -10, 10, -5, 1}, {6, 126, 630, 1950, 4680}, 32]
CoefficientList[Series[6 (10 x^2 + 16 x + 1) / (1 - x)^5, {x, 0, 33}], x] (* Vincenzo Librandi, Feb 11 2016 *)

a(n) = 3*(n+1)*(n+2)*(3*n+1)*(3*n+4)/4 \\ Felix Fröhlich, Jun 07 2016

G.f.: -6*(10*x^2 + 16*x + 1)/(x - 1)^5.
a(n) = Sum_{k = 0..n} (3*k + 1)(3*k + 2)(3*k + 3).
Sum {n>=0} 1/a(n) = 2*(sqrt(3)*Pi + 9*log(3) - 14)/15 = 0.1771878254287521...
a(n) mod 6 = 0.
a(n) = 6*A116689(n+1). - R. J. Mathar, Jun 07 2016
E.g.f.: 3*exp(x)*(8 + 160*x +256*x^2 + 96*x^3 + 9*x^4)/4. - Stefano Spezia, Apr 18 2023
Sum_{n>=0} (-1)^n/a(n) = 28/15 - 8*Pi/(15*sqrt(3)) - 16*log(2)/15. - Amiram Eldar, Apr 30 2023

A228889 a(n) = 3n(3n + 1)(3*n + 2).

Original entry on oeis.org

60, 336, 990, 2184, 4080, 6840, 10626, 15600, 21924, 29760, 39270, 50616, 63960, 79464, 97290, 117600, 140556, 166320, 195054, 226920, 262080, 300696, 342930, 388944, 438900, 492960, 551286, 614040, 681384, 753480, 830490, 912576, 999900, 1092624, 1190910

Offset: 1

Peter Bala, Sep 09 2013

Related sequences are A054776 and A097321.

Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

Cf. A054776, A097321, A228888.

[3*n*(3*n+1)*(3*n+2): n in [1..40]]; // Vincenzo Librandi, Sep 10 2013

Maple
```
seq(3*n*(3*n+1)*(3*n+2), n = 1..35);
```

CoefficientList[Series[6 (10 + 16 x + x^2)/(1 - x)^4, {x, 0, 40}], x] (* Vincenzo Librandi, Sep 10 2013 *)
Table[Times@@(3n+{0,1,2}),{n,40}] (* or *) LinearRecurrence[{4,-6,4,-1},{60,336,990,2184},40] (* Harvey P. Dale, Dec 20 2023 *)

a(n) = 3*n*(3*n + 1)*(3*n + 2) = 6*binomial(3*n + 2,3) = 6*A228888(n).
a(-n) = - A054776(n).
G.f.: 6*x*(10 + 16*x + x^2)/(1 - x)^4 = 60*x + 336*x^2 + 990*x^3 + ....
Sum {n >= 1} 1/a(n) = 3/4 - log(3)/4 - 1/12*sqrt(3)*Pi;
Sum {n >= 1} (-1)^n/a(n) = 3/4 - 2/3*log(2) - 1/18*sqrt(3)*Pi.

A119832 Bi-diagonal inverse of (3n)!/(3k)!.

Original entry on oeis.org

1, -6, 1, 0, -120, 1, 0, 0, -504, 1, 0, 0, 0, -1320, 1, 0, 0, 0, 0, -2730, 1, 0, 0, 0, 0, 0, -4896, 1, 0, 0, 0, 0, 0, 0, -7980, 1, 0, 0, 0, 0, 0, 0, 0, -12144, 1, 0, 0, 0, 0, 0, 0, 0, 0, -17550, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, -24360, 1

Offset: 0

Paul Barry, May 25 2006

Row sums are 1-A054776(n). Inverse of A119831.

			Triangle begins
1,
-6, 1,
0, -120, 1,
0, 0, -504, 1,
0, 0, 0, -1320, 1,
0, 0, 0, 0, -2730, 1,
0, 0, 0, 0, 0, -4896, 1,
0, 0, 0, 0, 0, 0, -7980, 1,
0, 0, 0, 0, 0, 0, 0, -12144, 1,
0, 0, 0, 0, 0, 0, 0, 0, -17550, 1,
0, 0, 0, 0, 0, 0, 0, 0, 0, -24360, 1

Column k has g.f. x^k(1-b(k+1)x) where b(n)=3n(3n-2)(3n-1)=A054776(n).

cp's OEIS Frontend

A006566 Dodecahedral numbers: a(n) = n*(3*n - 1)*(3*n - 2)/2.

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A268685 a(n) = 3*(n + 1)*(n + 2)*(3*n + 1)*(3*n + 4)/4.

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A228889 a(n) = 3*n*(3*n + 1)*(3*n + 2).

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A119832 Bi-diagonal inverse of (3n)!/(3k)!.

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A006566 Dodecahedral numbers: a(n) = n(3n - 1)(3n - 2)/2.

A268685 a(n) = 3(n + 1)(n + 2)(3n + 1)(3n + 4)/4.

A228889 a(n) = 3n(3n + 1)(3*n + 2).