a(k) = card { i*j, i <= k, j <= lcm(1,2,3...,k) }.

Terms

a(0) =1a(1) =3a(2) =12a(3) =29a(4) =176a(5) =198a(6) =1608a(7) =3519a(8) =11604a(9) =12500a(10) =152720a(11) =160970a(12) =2292000a(13) =2417700a(14) =2549904a(15) =5336115a(16) =97630080a(17) =101271000a(18) =2055670560a(19) =2125864116a(20) =2209916016a(21) =2291367000a(22) =55764302880a(23) =57138304410a(24) =297081542208