19381817300domain: NAppears in sequencesNumber of simsun permutations of {1,2,...,n} having at least one 321 pattern. A permutation p in S_n is said to be simsun if it has no double descents and with the hereditary property that when n, n-1, ..., 2, 1 are deleted in succession, the property of not having double descents is preserved after each deletion.at n=15A166298