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 A258156 Curl kernel sequence: a(n) is the number of independent constants on which an n-th-order tensor h can be shown to depend if the equation [curl (h nabla^{n-2}curl v)=0] is satisfied nontrivially for all vectors v. 0
 0, 6, 44, 183 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS To calculate a(n) has been difficult. So far a brute force (by hand!) approach has been the only fruitful method. That is, writing the equation of consideration in index notation, taking a Fourier transform and solving a rather large system of linear equations in 3^n unknowns. Based on observation, it is suspected that the sequence takes the form [0, n=2, 3^n - q(n), n>2], where q(n) is quadratic in n. The quadratic in question is hypothesized to be q(n)=(1/2)*(7*n^2-17*n+30). Writing a computer program to find further terms is desirable but beyond my expertise. LINKS EXAMPLE The case n = 2 is a special case since [curl (h curl v) = 0] is elliptic and so h = 0. CROSSREFS Sequence in context: A075337 A000561 A292057 * A182540 A309418 A203601 Adjacent sequences:  A258153 A258154 A258155 * A258157 A258158 A258159 KEYWORD nonn,more AUTHOR James Alexander Evans, May 22 2015 STATUS approved

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Last modified August 6 10:14 EDT 2020. Contains 336245 sequences. (Running on oeis4.)