Partial sums of A006431.

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =11a(5) =17a(6) =24a(7) =32a(8) =43a(9) =57a(10) =72a(11) =95a(12) =119a(13) =151a(14) =207a(15) =303a(16) =431a(17) =655a(18) =1039a(19) =1551a(20) =2447a(21) =3983a(22) =6031a(23) =9615a(24) =15759a(25) =23951a(26) =38287a(27) =62863a(28) =95631a(29) =152975