42319domain: NAppears in sequencesNumbers k such that the period of the continued fraction for sqrt(k) contains exactly 21 ones.at n=23A031789a(n) = 80*n^2 - 1.at n=22A158774Number of ordered triples (w,x,y) with all terms in {-n,...,-1,1,...,n} and w+3x+3y>0.at n=22A211625