a(n) = Sum_{0<=j<=i<=n} A027157(i, j).

Terms

a(0) =1a(1) =4a(2) =14a(3) =36a(4) =103a(5) =248a(6) =684a(7) =1624a(8) =4445a(9) =10524a(10) =28762a(11) =68060a(12) =185955a(13) =439984a(14) =1202072a(15) =2844144a(16) =7770361a(17) =18384884a(18) =50228454a(19) =118841812a(20) =324681887a(21) =768205608a(22) =2098776772a(23) =4965759176a(24) =13566706389a(25) =32099171980a(26) =87696568754a(27) =207492309516a(28) =566879531803