21217

Appears in sequences

• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 90 ones.at n=18A031858
• First differences of A037260.at n=42A037261
• Numerators of continued fraction convergents to sqrt(663).at n=7A042274
• Column 3 of triangle A055898.at n=11A055899
• Numbers k such that 3 + (integer formed from first k digits after decimal point in Pi) is prime.at n=8A058941
• Shallow diagonal of triangular spiral in A051682.at n=34A081275
• Third row of Pascal-(1,7,1) array A081582.at n=26A081593
• a(n) = 128*n^2 - 32*n + 1.at n=12A157331
• a(n) = 128*n^2 + 2528*n + 12481.at n=2A157436
• a(n) = 2*prime(n)^2 - 1.at n=26A179262
• Number of (n+3) X 9 binary arrays with every 4 X 4 subblock commuting with each horizontal and vertical neighbor 4 X 4 subblock.at n=11A188102
• T(n,k)=Hilltop maps: number of nXk binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 nXk array.at n=37A221446
• Hilltop maps: number of 2 X n binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 2 X n array.at n=7A221447
• Molien series for invariants of finite Coxeter group A_12.at n=53A266781
• Numbers of the form (k^2 - 2) / 2 where k - 1 and k + 1 are both odd composite numbers.at n=27A339480
• Composite numbers for which A324644(n)/A324198(n) = 2 and sigma(n) == 2 (mod 4).at n=20A371082
• Square array A(n,k), n>=0, k>=0, read by antidiagonals downwards, where column k is the expansion of 1/(1 - k*x) * Product_{j=0..k-1} (1 + j*x)/(1 - j*x).at n=58A383818