1,7

The row polynomials P(n,x):=sum(a(n,k)*x^k,k=0..p(n)-1), n>=1, appear in the numerator of the g.f. G(p(n),x) for the numbers N(p(n),m) of inequivalent m-bead necklaces of two colors with p(n) beads of one color and m-p(n) beads of the other color. Here p(n)=A000040(n) (prime numbers). Equivalently, N(p(n),m) counts inequivalent necklaces with p(n) beads which are labeled with nonnegative numbers, such that the sum of the labels is m. For a proof of this equivalent formulation see a comment in A032191. Inequivalence is meant with respect to the cyclc group C_p(n).

This necklace g.f. is G(p(n),x)= P(n,x)/((1-x^p(n))*(1-x)^(p(n)-1)), n>=1. The row polynomials P(n,x) are defined above. This g.f. is Z(C_p(n),x), the two variable (x[1] and x[p(n)]) cycle index polynomial for the cyclic group of prime order p(n), with substitution x[1]->1/(1-x^1)and x[p(n)]->1/(1-x^p(n)). This follows by Polya enumeration if the above mentioned labeled necklace problem is solved.

The row length sequence for this array a(n,k) is A000040(n) (n-th prime number), [2, 3, 5, 7, 11, 13, 17, 19, 23, 29,...].

The rows of this signed array are symmetric: a(n,k)=a(n,p(n)-1-k), n>=2, k=0..(p(n)-1)/2. See the explicit formula below.

The formulae for a(n,k), given below, produces in fact integers.

G.f. for column k, k>=0 (without leading zeros): (sum(A103718(k,m)*p(n)^m,m=0..k)/k! produces for all n> pi(n) integers, where pi(n):=A000720(n), primes not exceeeding n.

W. Lang, Array and more comments.

a(n, k)= (1 + ((-1)^k)*(p(n)-1)*binomial(p(n)-1, k))/p(n), with p(n):= A000040(n) (n-th prime).

a(n, k)= sum(A103718(k, m)*p(n)^m, m=0..k)/k!, (row polynomials of triangle A103718 with x=p(n), divided by k!).

[1,-0]; [1,-1,1]; [1,-3,5,-3,1]; [1,-5,13,-17,13,-5,1]; [1,-9,41,-109,191,-229,191,-109,41,-9,1]; ...

n=3: G(p(3),x)=G(5,x)=(1-3*x+5*x^2-3*x^3+1*x^4)/((1-x^5)*(1-x)^4) generates the necklace sequence A008646.

A103718(3,m), m=0..3, is [17,-17,7,-1]. Therefore (17-17*p(n)+7*p(n)^2-1*p(n)^3 )/3! gives, for n>=1, the third column [ -3,-17,-109,...].

The unsigned column sequences are for k=0..10: A000012 (powers of 1), A040976 (primes p(n)-2), A103729 - A103914, A103915.

Sequence in context: A114865 A096196 A076824 this_sequence A023505 A021743 A057023

Adjacent sequences: A103725 A103726 A103727 this_sequence A103729 A103730 A103731

sign,easy,tabf

Wolfdieter Lang (wolfdieter.lang_AT_physik_DOT_uni-karlsruhe_DOT_de), Feb 24 2005