Sum of binary numbers with n 1's and two (possibly leading) 0's.

Terms

a(0) =0a(1) =7a(2) =45a(3) =186a(4) =630a(5) =1905a(6) =5355a(7) =14308a(8) =36828a(9) =92115a(10) =225225a(11) =540606a(12) =1277874a(13) =2981797a(14) =6881175a(15) =15728520a(16) =35651448a(17) =80215911a(18) =179306325a(19) =398458690a(20) =880803630a(21) =1937768217a(22) =4244635395a(23) =9261022956a(24) =20132658900a(25) =43620761275