6917400domain: NAppears in sequencesk-imperfect numbers for some k >= 1.at n=23A1277243-imperfect numbers.at n=15A127726a(n) = A057863(n+1) * Sum_{k=0..n}(k! / (2*k+1)!!).at n=4A279886Expansion of e.g.f. exp((exp(x) - 1)^5).at n=10A375773