21870

Appears in sequences

• a(n) = 10*3^n.at n=7A005052
• Number of irreducible systems of meanders.at n=7A006664
• McKay-Thompson series of class 9A for Monster.at n=10A007266
• Theta series of D_15 lattice.at n=2A022046
• Theta series of D*_15 lattice.at n=16A022068
• Numbers of form 3^i*10^j, with i, j >= 0.at n=26A025616
• Weight enumerator of [ 40,19,10 ] shortened QR code.at n=7A030645
• Triangle whose (i,j)-th entry is binomial(i,j)*3^(i-j)*9^j.at n=17A038227
• Triangle whose (i,j)-th entry is binomial(i,j)*9^(i-j)*3^j.at n=18A038293
• Sums of 2 distinct powers of 3.at n=43A038464
• McKay-Thompson series of class 9A for the Monster group with a(0) = 3.at n=10A045491
• a(n) = Sum_{i=0..floor(n/2)} T(2i,n-2i), array T as in A049735.at n=27A049738
• Diagonal of table A062104.at n=10A062107
• Number of ternary trees (A001764) with n nodes and maximal diameter.at n=8A064017
• Ordered m for which m = k^3*a*b*(a^4 - b^4) determine (unique) solution triples(k,a,b), where k=1,2,3,... and (a,b) are coprime pairs, not both odd (i.e., of opposite parity).at n=19A081779
• Number of (k,m,n)-antichains of multisets with k=3 and m=2.at n=5A084874
• Smallest number having exactly n ones in binary representation and also exactly n prime factors (counted with multiplicity).at n=8A115156
• a(n) = (n^3+n)*9^n.at n=3A128074
• (n^2-n)*3^n.at n=6A128797
• Expansion of (eta(q^3)^2 / (eta(q) * eta(q^9)))^6 in powers of q.at n=10A131985