21523360

Appears in sequences

• a(n) = (3^n - 1)/2.at n=16A003462
• Numbers that are repdigits in base 3.at n=31A048328
• a(n) = a(n-1) + 3*a(n-2) - 3*a(n-3), with a(0)=a(1)=1, a(2)=4.at n=30A052993
• a(n) = a(n-1) + 3*a(n-2) - 3*a(n-3), with a(0)=a(1)=1, a(2)=4.at n=31A052993
• Number of primitive (aperiodic) word structures of length n using a 3-ary alphabet.at n=16A056274
• a(n) = floor(9^9/n).at n=17A057071
• a(n) = (3^(2^n)-1)/2.at n=4A059918
• a(n) = (-1)^n * (3^n - 1)/2.at n=16A076040
• a(n) = ((2n+1)*3^n - 1)/2.at n=12A079272
• Maximal term in Collatz-iteration started at 3^n-1.at n=14A087971
• a(n) = floor(3^n / n).at n=17A092763
• Expansion of (1+3x)/((1-x^2)(1-3x^2)).at n=30A094025
• Modulo 2 binomial transform of 3^n.at n=15A100307
• a(n) = Sum_{j=0..15} n^j.at n=3A105312
• Row sums in A112668.at n=15A110737
• Expansion of x*(1+x+2*x^3) / ((x-1)*(1+x)*(3*x^2-1)).at n=31A120463
• a(n) = 3*a(n-1) - a(n-3) + 3*a(n-4), with initial values 2,5,13,40.at n=15A133448
• a(n) = 3*a(n-1) - a(n-3) + 3*a(n-4), with initial values 2,4,13,40.at n=15A133453
• First differences of A140298.at n=49A140313
• First differences of A140298.at n=50A140313