21000

Appears in sequences

• Number of carbon (rooted) trees with n carbon atoms = unordered 4-tuples of ternary trees.at n=14A000678
• Smallest natural number requiring n words in English (as spoken in England).at n=2A001167
• Squares written in base 4.at n=24A001739
• 11-gonal (or hendecagonal) pyramidal numbers: a(n) = n*(n+1)*(3*n-2)/2.at n=24A007586
• Area of more than one Pythagorean triangle.at n=18A009127
• Even octagonal numbers: a(n) = 4*n*(3*n-1).at n=42A014642
• Numbers k such that k^2 has digits in nonincreasing order.at n=37A028821
• Number of diagonal dissections of an n-gon into 3 regions.at n=20A033275
• Triangle of coefficients of certain polynomials (exponents in decreasing order).at n=51A033842
• Decimal part of a(n)^(1/3) starts with a 'nine digits' anagram.at n=6A034278
• Triangle T(n,k) = k! * Stirling1(n,k), 1<=k<=n.at n=25A048594
• Triangle of coefficients of certain polynomials (exponents in increasing order), equivalent to A033842.at n=48A049323
• Numbers whose sum of digits is 3.at n=33A052217
• Expansion of e.g.f.: -(log(1-x))^5.at n=7A052767
• Max_{k=0..n} k!*|Stirling1(n,k)|.at n=7A058583
• a(n) = gcd(Phi(n!), Phi(n^n), Phi(lcm(1..n))).at n=34A064449
• Areas of integer Heronian triangles [A068967(n), prime(A068967(n)), A068968(n)].at n=9A068969
• Numbers k not in A065036 but such that tau(k) = omega(k)^3.at n=19A074853
• Coefficients of certain polynomials (rising powers).at n=23A075181
• a(n) = n * [1 + sum(k=1 to n-1) prime(k)].at n=24A083719