21554

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 12.at n=16A031600
• Third differences of Catalan numbers A000108.at n=8A033434
• Coordination sequence for B_13 lattice.at n=2A107546
• Number of ways to write n as an ordered sum of 1s, 2s, 3s and 4s such that no 2 precedes any 1 and no 3 precedes any 1 or 2.at n=26A123569
• Number of binary strings of length n with equal numbers of 0001 and 1110 substrings.at n=16A164165
• G.f.: (1+x+x^2+x^3)/(1-x^2-2*x^3-x^4+x^6).at n=22A234273
• p-INVERT of the positive integers, where p(S) = (1 - S)(1 - S^2).at n=9A290929
• Number of compositions (ordered partitions) of n into an odd number of triangular numbers.at n=26A339417