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 A113062 Expansion of theta series of hexagonal net with respect to a node. 7
 1, 3, 0, 6, 3, 0, 0, 6, 0, 6, 0, 0, 6, 6, 0, 0, 3, 0, 0, 6, 0, 12, 0, 0, 0, 3, 0, 6, 6, 0, 0, 6, 0, 0, 0, 0, 6, 6, 0, 12, 0, 0, 0, 6, 0, 0, 0, 0, 6, 9, 0, 0, 6, 0, 0, 0, 0, 12, 0, 0, 0, 6, 0, 12, 3, 0, 0, 6, 0, 0, 0, 0, 0, 6, 0, 6, 6, 0, 0, 6, 0, 6, 0, 0, 12, 0, 0, 0, 0, 0, 0, 12, 0, 12, 0, 0, 0, 6, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The hexagonal net is the familiar 2-dimensional honeycomb (not a lattice) in which each node has 3 neighbors. Cubic AGM theta functions: a(q) (see A004016), b(q) (A005928), c(q) (A005882). REFERENCES A. F. Wells, Structural Inorganic Chemistry, Oxford, 5th ed., 1984; see Fig. 3.9(a.1). LINKS T. D. Noe, Table of n, a(n) for n = 0..1000 G. L. Hall, Comment on the paper "Theta series and magic numbers for diamond and certain ionic crystal structures" [J. Math. Phys. 28, 1653 (1987)]. Journal of Mathematical Physics; Sep. 1988, Vol. 29 Issue 9, pp. 2090-2092. - From N. J. A. Sloane, Dec 18 2012 N. J. A. Sloane, Theta series and magic numbers for diamond and certain ionic crystal structures, J. Math. Phys. 28 (1987), 1653-1657. FORMULA Moebius transform is period 9 sequence [ 3, -3, 3, 3, -3, -3, 3, -3, 0, ...]. Expansion of a(q^3) + c(q^3) in powers of q where a(), c() are cubic AGM theta functions. - Michael Somos, Aug 15 2006 a(n) = 3*b(n) where b(n) is multiplicative and b(p^e) = 2 if p = 3 and e>0, b(p^e) = e+1 if p == 1 (mod 6), b(p^e) = (1+(-1)^e)/2 if p == 2, 5 (mod 6). a(3*n + 2) = 0. a(3*n + 1) = A005882(n) = A033685(3*n + 1) = -A005928(3*n + 1). a(3*n) = A004016(n) = A005928(3*n). 3*a(n) = A113063(n) if n>0. EXAMPLE G.f. = 1 + 3*q + 6*q^3 + 3*q^4 + 6*q^7 + 6*q^9 + 6*q^12 + 6*q^13 + 3*q^16 + ... MATHEMATICA a[0] = 1; a[n_] := 3*DivisorSum[n, {0, 1, -1, 1, 1, -1, -1, 1, -1}[[Mod[#, 9]+1]]&]; Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Nov 04 2015, after 1st PARI script *) PROG (PARI) {a(n) = if( n<1, n==0, 3 * sumdiv(n, d, [ 0, 1, -1, 1, 1, -1, -1, 1, -1][d%9+1]))}; (PARI) {a(n) = local(A, p, e); if( n<1, n==0, A = factor(n); 3 * prod(k=1, matsize(A)[1], if(p=A[k, 1], e=A[k, 2]; if(p==3, 2, if(p%6==1, e+1, !(e%2))))))}; (PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); abs( polcoeff( eta(x + A)^3 / eta(x^3 + A), n)))}; (PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x + A)^3 + 6 * x * eta(x^9 + A)^3) / eta(x^3 + A), n))}; /* Michael Somos, Aug 15 2006 */ CROSSREFS Cf. A004016, A005882, A005928, A033685, A113063. Sequence in context: A011079 A226535 A005928 * A259659 A005889 A095712 Adjacent sequences:  A113059 A113060 A113061 * A113063 A113064 A113065 KEYWORD nonn AUTHOR Michael Somos, Oct 13 2005; definition corrected Oct 17 2005 STATUS approved

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Last modified November 14 11:04 EST 2018. Contains 317182 sequences. (Running on oeis4.)