1658385domain: NAppears in sequences3*n*(9n + 2)*(18n - 1), where n runs through the odd numbers 1, 3, 5,...at n=7A213071Nonsquarefree numbers n = p_1^s_1...p_m^s_m (m > 1) such that (p_i^s_i - 1) | n-1 for all 0 < i <= m.at n=23A292815