135861domain: NAppears in sequencesNumbers k such that phi(k)*sigma(k) is a triangular number.at n=16A115911Number of (w,x,y,z) with all terms in {1,...,n} and w+x<y+z.at n=23A212523Number of regions after generation n of Conant's dissection of a square when dissected with diagonal lines.at n=20A334630