21357

Appears in sequences

• From a nim-like game.at n=37A003413
• Numbers having four 5's in base 8.at n=6A043444
• a(n) = A104908(n) - 10*A104863(n).at n=33A104909
• Numbers n such that n^6 + 272 is prime.at n=29A161998
• a(n) = (2*n^3 + 5*n^2 - 11*n)/2.at n=26A162257
• Number x such that usigma(x) = (-1)sigma(x), where usigma(x) is the sum of unitary divisors of x (A034448) and (-1)sigma(x) is defined in A049060 .at n=3A258101
• Sum of the lengths of the arithmetic progressions in {1,2,3,...,n}, including trivial arithmetic progressions of lengths 1 and 2.at n=41A264100
• Expansion of e.g.f. (1/x) * Series_Reversion( x / (1 + 3*x*exp(x))^(1/3) ).at n=7A380081
• a(n) = Sum_{k=0..floor(n/4)} 2^k * 3^(n-3*k) * binomial(n-2*k,k) * binomial(n-3*k,k).at n=8A390830