21610

Appears in sequences

• a(n) is the integer (reduced squarefree) under the square root obtained when the inverse of a variant of Minkowski's question mark function is applied to the n-th ratio A007305(n+1)/A007306(n+1) in the left-hand subtree of Stern-Brocot tree and zero when it results a rational value.at n=73A065936
• a(n) = 9*7^n+1.at n=4A199487
• Beach-Williams Pell numbers of type k^2 + 1.at n=17A212082
• Number of (n+1) X (6+1) 0..1 arrays with nondecreasing min(x(i,j), x(i,j-1)) in the i direction and nondecreasing absolute value of x(i,j)-x(i-1,j) in the j direction.at n=3A250795
• T(n,k)=Number of (n+1)X(k+1) 0..1 arrays with nondecreasing min(x(i,j),x(i,j-1)) in the i direction and nondecreasing absolute value of x(i,j)-x(i-1,j) in the j direction.at n=39A250797
• Number of (4+1) X (n+1) 0..1 arrays with nondecreasing min(x(i,j),x(i,j-1)) in the i direction and nondecreasing absolute value of x(i,j)-x(i-1,j) in the j direction.at n=5A250801
• Number of (n+3)X(4+3) 0..1 arrays with each row divisible by 9 and column not divisible by 9, read as a binary number with top and left being the most significant bits.at n=0A262818
• T(n,k)=Number of (n+3)X(k+3) 0..1 arrays with each row divisible by 9 and column not divisible by 9, read as a binary number with top and left being the most significant bits.at n=6A262819
• Number of (1+3)X(n+3) 0..1 arrays with each row divisible by 9 and column not divisible by 9, read as a binary number with top and left being the most significant bits.at n=3A262820
• a(n) = number of decimal digits of A007505(n).at n=39A275247
• Number of irreducible involutions of length n avoiding the pattern {123}.at n=15A278025
• Numbers d > 1 such that the class number of Q(sqrt(d)) is strictly greater than the class number of Q(sqrt(m)) for all m < d.at n=11A283658
• Indices of records in A360519.at n=48A361108
• Triangle read by rows: T(n,k) is the number of k-dimensional faces of the n-dimensional Kunz cone, 0 <= k <= n.at n=61A364856
• Expansion of (1/x) * Series_Reversion( x * (1-x^2/(1-x))^3 ).at n=9A369013
• Place n equally spaced points around the circumference of a circle and then, for each pair of points, draw two distinct circles, whose radii are the same as the first circle, such that both points lie on their circumferences. The sequence gives the total number of vertices formed.at n=20A371373
• a(n) = Sum_{k=0..n} binomial(k+4,4) * binomial(k,n-k)^2.at n=7A377152
• Numbers k such that k-1 is a perfect square and k+1 is prime.at n=16A392249