3879876

Appears in sequences

• a(n) = (2n+1)!/n!^2.at n=10A002457
• a(n+1) = a(n)/n if n|a(n) else a(n)*n, a(1) = 1.at n=21A008336
• Expansion of (1-4*x)^(21/2).at n=10A020933
• Denominator of n * n-th harmonic number.at n=19A027611
• First numerator and then denominator of central elements of Leibniz's Harmonic Triangle.at n=21A046212
• Swinging factorial, a(n) = 2^(n-(n mod 2))*Product_{k=1..n} k^((-1)^(k+1)).at n=21A056040
• a(n) = n!/(k!)^2, where k is the largest number such that (k!)^2 divides n!.at n=20A056042
• Denominator of Sum_{i+j+k=n, i,j,k>=1} (i*j)/k.at n=23A076175
• Smallest integer value of n!/(2!3!...p!), where denominator contains product of factorials of primes in increasing order.at n=20A088302
• a(n) = 42*binomial(n,10).at n=19A088626
• a(n) = n * binomial(n-1, floor((n-1)/2)) = n * max_{i=0..n} binomial(n-1, i).at n=21A100071
• Denominator of partial sums of a certain series.at n=4A101630
• a(n) = binomial(n+4,4) * binomial(n+9,4).at n=10A104678
• (n-1)! divided by (product phi(d)! ; d divides n).at n=21A120066
• Triangle T(n,k) = lcm(1,...,2*n+2)/((k+1)*binomial(2*k+2,k+1)).at n=47A120101
• Number triangle T(n,k) = lcm(1,..,2*n+2)/lcm(1,..,2*k+2).at n=47A120105
• Triangle read by rows: T(n, k) = v(n, k)*((1/v(n, k)) mod prime(k)), where v(n, k) = (Product_{j=1..n} prime(j))/prime(k), n >= 1, 1 <= k <= n.at n=30A240673
• a(n) = 2^n*binomial((n + 1 + (n mod 2))/2, 1/2).at n=20A242172
• Lexicographically earliest sequence such that for any n>1, n=u*v, where u/v = a(n)/a(n-1) in reduced form.at n=20A260850
• a(n) = A(n) if n is even else a(n) = A(n)*(n-1)/(n+1) with A(n) = ((n-1)!/ floor((n-1)/2)!^2).at n=21A274707