Values of k in A071580.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =10a(6) =12a(7) =10a(8) =21a(9) =25a(10) =70a(11) =670a(12) =239a(13) =2115a(14) =586a(15) =1619a(16) =26800a(17) =2505a(18) =99019a(19) =40903a(20) =285641a(21) =67166a(22) =1852765