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A231846 Polynomials for total Pontryagin classes. Refinement of double Pochhammer triangle. 3
1, 1, 2, 1, 8, 6, 1, 48, 32, 12, 12, 1, 384, 240, 160, 80, 60, 20, 1, 3840, 1440, 640, 120, 2304, 960, 720, 180, 160, 30, 1, 46080, 16128, 13440, 3360, 26880, 10080, 4480, 840, 8064, 3360, 1680, 420, 280, 42, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

The W. Lang link in A036039 explicitly gives the first several cycle index polynomials for the symmetric group S_n, or the partition polynomials for the refined Stirling numbers of the first kind. In line with the discussion in the Fecko link, null the indeterminates with odd indices, divide the 2n-th partition polynomial by the double factorial of odd numbers given in A001147, and re-index. The sum of the resulting row coefficients are also equal to A001147.

LINKS

Table of n, a(n) for n=0..44.

M. Fecko, Selected topological concepts used in physics pp. 37-41 and 56-58.

Wikipedia, Pontryagin class

Y. Zhang, A brief introduction to characteristic classes from the differentiable viewpoint p. 27.

FORMULA

From Tom Copeland, Oct 11 2016: (Start)

A generating function for the polynomials PB_n[b_2,b_4,..,b_(2n)] of this array is

exp[b_2 y^2/2 + b_4 y^4/4 + b_6 y^6/6 + ...] = Sum_{n >= 0} PB_n y^(2n) / A000165(n) = Sum_{n >= 0} St1[2n,0,b_2,0,b_4,0,..,b_(2n)] y^(2n) / (2n)! = Sum_{n >= 0} PB_n *(y/sqrt(2))^(2n) / n! with b_n = Tr(F^n), as in the examples, and St1(n,b_1,b_2,..,b_n), the partition polynomials of A036039. Then St1[2n,0,b_2,0,b_4,..,0,b_(2n)] = A001147(n) * PB_n.

The polynomials PC_n(c_1,c_2,..,c_n) of this array with c_k = b_(2k) are an Appell sequence in the indeterminate c_1 with lowering operator L = d/d(c_1), i.e., L*PC_n(c_1,..,c_n) = d(PC_n)/d(c_1) = n * PC_(n-1)[c_1,..,c_(n-1)].

With [PC.(c_1,c_2,..)]^n = PC_n(c_1,..,c_n), the e.g.f. is G(t,c_1,c_2,..) = exp[t*PC.(0,c_2,c_3,..)] * exp(t*c_1) = exp{t*[c_1 + PC.(0,c_2,c_3,..)]} = exp[t*PC.(c_1,c_2,..)] = exp[(1/2) * sum_{n > 0} c_n (2t)^n/n ] = exp[-log(1-2c.t) / 2], where, umbrally, (c.)^n = c_n.

The raising operator is R = d[log(G(L,c_1,c_2,..))]/dL = sum_{n >= 0} 2^n * c_(n+1) * (d/dc_1)^n = c./(1-2c.L), umbrally. R PC_n(c_1,..,c_n) = P_(n+1)[c_1,..,c_(n+1)].

Another generator: G(L,0,c_2,c_3,..) (c_1)^n = PC_n(c_1,c_2,..,c_n).

The Appell umbral compositional inverse sequence UPC_n to the PC_n sequence has e.g.f. UG(t,c_1,c_2,..) = [1 / G(t,0,c_2,c_3,..)] *  exp(t*c_1) with lowering operator L, as above, and raising operator RU = c_1 - sum_{n > 0} 2^n * c_(n+1) * (d/dc_1)^n. It follows that UPC_n(c_1,c_2,..,c_n) = PC_n(c_1,-c_2,..,-c_n) and PC_n(PC.(c_1,c_2,..),-c_2,-c_3,..) = PC_n(PC.(c_1,-c_2,-c_3,..),c_2,c_3,..) = (c_1)^n, e.g., PC_2(PC.(c_1,-c_2,..),c_2) = 2 c_2 + (PC.(c_1,-c_2,..))^2 = 2 c_2 + PC_2(c_1,-c_2) = 2 c_2 + 2 (-c_2) + (c_1)^2 = (c_1)^2.

Letting c_1 = x and all other c_n = 1 gives the row polynomials of A055140.

(End)

EXAMPLE

In terms of the trace of a curvature form Tr(F^n)={n} or indeterminates c_n=[n]:

P_0 = 1,

P_1 = Tr(F^2) = {2}

    = c_1 = [1],

P_2 = 2Tr(F^4)+Tr(F^2)^2 = 2{4}+{2}^2

    = 2c_2+ (c_1)^2 = 2[2]+[1]^2,

P_3 = 8Tr(F^6)+6Tr(F^2)Tr(F^4)+Tr(F^6)= 8{6}+6{2}{4}+{6}

    = 8c_3+6c_1 c_2+(c_1)^3 = 8[3]+6[1][2]+[1]^3,

P_4 = 48{8}+32{2}{6}+12{4}^2+12{2}^2{4}+{2}^4

    = 48[4]+32[1][3]+12[2]^2+12[1]^2[2]+[1]^4,

P_5 = 384{10}+240{2}{8}+160{4}{6}+80{2}^2{6}

      + 60{2}{4}^2+20{2}^3{4}+{2}^5

    = 384[5]+240[1][4]+160[2][3]+80[1]^2[3]

      + 60[1][2]^2+20[1]^3[2]+[1]^5

P_6 = 3840[6]+1440[2][4]+640[3]^2+120[2]^3+2304[1][5]

      + 960[1][2][3]+720[1]^2[4]+180[1]^2[2]^2+160[1]^3[3]+30[1]^4[2]+[1]^6

P_7 = 46080[7]+16128[2][5]+13440[3][4]+3360[2]^2[3]+26880[1][6]+10080[1][2][4]+4480[1][3]^2+840[1][2]^3+8064[1]^2[5]+3360[1]^2[2][3]+1680[1]^3[4]+420[1]^3[2]^2+280[1]^4[3]+42[1]^5[2]+[1]^7

....

Summing over partitions with the same number of blocks gives the unsigned double Pochhammer triangle A039683. Row sums are A001147. Multiplying P_n by the row sum gives the 2n-th partition polynomial of A036039 with its odd-indexed indeterminates nulled.

For c_1 = c_2 = x and c_n = 0 otherwise, see A119275.

CROSSREFS

Cf. A000165, A001147, A036039, A055140, A119275.

Sequence in context: A142336 A193735 A114193 * A039683 A318389 A108084

Adjacent sequences:  A231843 A231844 A231845 * A231847 A231848 A231849

KEYWORD

nonn,tabf,more

AUTHOR

Tom Copeland, Nov 14 2013

EXTENSIONS

Polynomials P_6 and P_7 added by Tom Copeland, Oct 11 2016

STATUS

approved

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Last modified June 1 11:05 EDT 2020. Contains 334762 sequences. (Running on oeis4.)