21700

Appears in sequences

• a(n) = Sum_{k=0..5} binomial(n,k).at n=20A006261
• a(n) = dot_product(1,2,...,n)*(6,7,...,n,1,2,3,4,5).at n=36A026046
• a(n) = n^3 + (n+1)^3 + (n+2)^3 + (n+3)^3.at n=16A027603
• Numbers k such that the sum of the squares of the divisors of k is divisible by k.at n=31A046762
• a(n) = Sum_{k=0..n} binomial(4*n,k).at n=5A066381
• Numbers n such that n*sigma(n) is a perfect square.at n=14A069070
• Numbers k such that the harmonic mean of the divisors of k is the square of a rational number.at n=10A074266
• Numbers k such that 2^(k+1) - 1 is prime.at n=24A090748
• Exponents m such that 1-A065395(2^m) is a power of 2, where A065395(n) = sigma(phi(n)) - phi(sigma(n)).at n=29A092591
• Number of partitions of n with rank 3 (the rank of a partition is the largest part minus the number of parts).at n=55A101200
• Nonnegative values x of solutions (x, y) to the Diophantine equation x^2+(x+833)^2 = y^2.at n=32A129010
• Coefficients of the sixth-order mock theta function psi_{-}(q).at n=30A153252
• Expansion of e.g.f. x*exp(x)*exp(x*exp(x)).at n=7A185298
• Number of n X 4 0..1 arrays avoiding 0 0 0 and 1 1 1 horizontally and 0 0 1 and 1 0 1 vertically.at n=31A208375
• Numbers whose numerator and denominator of the harmonic mean of their divisors are both 5-smooth numbers.at n=50A348868
• Numbers k such that the sum of the squares of the odd divisors of k (A050999) is divisible by k.at n=17A355543
• Expansion of e.g.f. A(x,y) satisfying A(x,y) = Sum_{n>=0} (A(x,y)^n + y)^n * x^n/n!, as a triangle read by rows.at n=34A361540
• a(n) is the number of positive integer solutions of n*x*y*z*v*w = (x + n) * (y + n) * (z + n) * (v + n) * (w + n), x <= y <= z <= v <= w.at n=22A381644
• a(n) is the number of possible choices for the first n terms of a "mean-central" sequence, where a monotonically increasing sequence of positive integers {b(n)} is called "mean-central" if for each positive integer k, the arithmetic mean of the first b(k) terms is exactly b(k).at n=28A383192