= One-dimensional cosmological density kernel
{title2=$F_{n,s}(q_1,\ldots,q_n)$}
For plane-parallel pressureless matter in an <Einstein-de Sitter universe>, before <shell crossing>, the symmetrized growing-mode <standard perturbation theory density kernel> is
$$
F_{n,s}(q_1,\ldots,q_n)=\frac{(q_1+\cdots+q_n)^n}{n!q_1\cdots q_n}.
$$
In particular $F_{2,s}=(q_1+q_2)^2/(2q_1q_2)$. An unsymmetrized representation of the one-dimensional <beta mode-coupling kernel> is $(q_1+q_2)/q_1$; its symmetric part is the expression above.
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