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A071232 a(n) = (n^6 + n^3)/2. 2
0, 1, 36, 378, 2080, 7875, 23436, 58996, 131328, 266085, 500500, 886446, 1493856, 2414503, 3766140, 5697000, 8390656, 12071241, 17009028, 23526370, 32004000, 42887691, 56695276, 74024028, 95558400, 122078125, 154466676, 193720086, 240956128, 297423855, 364513500 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Number of unoriented rows of length 6 using up to n colors. For a(0)=0, there are no rows using no colors. For a(1)=1, there is one row using that one color for all positions. For a(2)=36, there are 2^6=64 oriented arrangements of two colors. Of these, 2^3=8 are achiral. That leaves (64-8)/2=28 chiral pairs. Adding achiral and chiral, we get 36. - Robert A. Russell, Nov 14 2018

For n > 0, a(2n+1) is the number of non-isomorphic 8C_m-snakes, where m = 2n+1 or m = 2n (for n>=2). A kC_n-snake is a connected graph in which the k >= 2 blocks are isomorphic to the cycle C_n and the block-cutpoint graph is a path. - Christian Barrientos, May 16 2019

REFERENCES

C. Barrientos, Graceful labelings of cyclic snakes, Ars Combin., 60 (2001), 85-96.

T. A. Gulliver, Sequences from Arrays of Integers, Int. Math. Journal, Vol. 1, No. 4, pp. 323-332, 2002.

T. A. Gulliver, Sequences from Cubes of Integers, Int. Math. Journal, 4 (2003), 439-445.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..2000

Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).

FORMULA

a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7); a(0)=0, a(1)=1, a(2)=36, a(3)=378, a(4)=2080, a(5)=7875, a(6)=23436. - Harvey P. Dale, Nov 06 2011

G.f.: x*(28*x^4 + 155*x^3 + 147*x^2 + 29*x + 1)/(1-x)^7. - Colin Barker, Oct 12 2012

From Robert A. Russell, Nov 14 2018: (Start)

a(n) = (A001014(n) + A000578(n)) / 2 = (n^6 + n^3) / 2.

a(n) = A001014(n) - A085744(n) = A085744(n) + A000578(n).

G.f.: (Sum_{j=1..6} S2(6,j)*j!*x^j/(1-x)^(j+1) + Sum_{j=1..3} S2(3,j)*j!*x^j/(1-x)^(j+1)) / 2, where S2 is the Stirling subset number A008277.

G.f.: x*Sum_{k=0..5} A145882(6,k) * x^k / (1-x)^7.

E.g.f.: (Sum_{k=1..6} S2(6,k)*x^k + Sum_{k=1..3} S2(3,k)*x^k) * exp(x) / 2, where S2 is the Stirling subset number A008277.

For n>6, a(n) = Sum_{j=1..7} -binomial(j-8,j) * a(n-j). (End)

E.g.f.: x*(2 +34*x +91*x^2 +65*x^3 +15*x^4 +x^5)*exp(x)/2. - G. C. Greubel, Nov 15 2018

MATHEMATICA

Table[(n^6+n^3)/2, {n, 0, 40}] (* or *) LinearRecurrence[{7, -21, 35, -35, 21, -7, 1}, {0, 1, 36, 378, 2080, 7875, 23436}, 40] (* Harvey P. Dale, Nov 06 2011 *)

PROG

(MAGMA) [(n^6 + n^3)/2: n in [0..50]]; // Vincenzo Librandi, Jun 14 2011

(PARI) vector(50, n, n--; (n^6 + n^3)/2) \\ G. C. Greubel, Nov 15 2018

(Sage) [(n^6 + n^3)/2 for n in range(50)] # G. C. Greubel, Nov 15 2018

(GAP) List([0..50], n -> (n^6 + n^3)/2); # G. C. Greubel, Nov 15 2018

CROSSREFS

Row 6 of A277504.

Cf. A001014 (oriented), A085744 (chiral), A000578 (achiral).

Sequence in context: A244795 A222492 A203282 * A135828 A250805 A254644

Adjacent sequences:  A071229 A071230 A071231 * A071233 A071234 A071235

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jun 11 2002

STATUS

approved

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Last modified April 16 18:53 EDT 2021. Contains 343050 sequences. (Running on oeis4.)