object Paraffins extends App { val (nMax, nBranches) = (250, 4) val rooted, unrooted = Array.tabulate(nMax + 1)(i => if (i < 2) BigInt(1) else BigInt(0)) val (unrooted, c) = (rooted.clone(), new Array[BigInt](nBranches)) for (n <- 1 to nMax) { def tree(br: Int, n: Int, l: Int, inSum: Int, cnt: BigInt): Unit = { var sum = inSum for (b <- br + 1 to nBranches) { sum += n if (sum > nMax || (l * 2 >= sum && b >= nBranches)) return if (b == br + 1) c(br) = rooted(n) * cnt else { c(br) = c(br) * (rooted(n) + BigInt(b - br - 1)) c(br) = c(br) / BigInt(b - br) } if (l * 2 < sum) unrooted(sum) = unrooted(sum) + c(br) if (b < nBranches) rooted(sum) = rooted(sum) + c(br) for (m <- n - 1 to 1 by -1) tree(b, m, l, sum, c(br)) } } def bicenter(s: Int): Unit = if ((s & 1) == 0) { val halves = rooted(s / 2) unrooted(s) = unrooted(s) + ((halves + BigInt(1)) * halves >> 1) } tree(0, n, n, 1, BigInt(1)) bicenter(n) println(f"$n%3d: ${unrooted(n)}%s") } }