Sum_{k=1..n} floor(n*(n-1)/(2*k)).

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =12a(5) =22a(6) =35a(7) =53a(8) =74a(9) =101a(10) =129a(11) =162a(12) =202a(13) =244a(14) =292a(15) =344a(16) =403a(17) =463a(18) =527a(19) =601a(20) =676a(21) =762a(22) =844a(23) =937a(24) =1035a(25) =1138a(26) =1245a(27) =1355a(28) =1476a(29) =1597