21838

Appears in sequences

• (Product of primes <= n) - 2^(n-1).at n=13A068511
• Generalized Jacobsthal numbers.at n=15A083579
• a(n) = 3*a(n-1) - a(n-2) - 3*a(n-3) + 2*a(n-4).at n=14A084172
• Numbers n such that sigma(2*phi(n)) = 2*sigma(n).at n=12A137733
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, 0, 0), (-1, 1, 1), (0, -1, 1), (0, 1, 0), (1, 1, -1)}.at n=10A148210
• Triangle read by rows: T(n,k) = 1 + (q-binomial coefficient [n,k] for q=4) - binomial(n,k).at n=37A176422
• Triangle read by rows: T(n,k) = 1 + (q-binomial coefficient [n,k] for q=4) - binomial(n,k).at n=43A176422
• The number of vertices formed by straight line segments mutually connecting all vertices of a semicircular polygon defined in A333642.at n=25A330913