a(n) = (A102877(n+1) - A102877(n))/2.

Terms

a(0) =0a(1) =1a(2) =2a(3) =7a(4) =20a(5) =61a(6) =180a(7) =543a(8) =1622a(9) =4873a(10) =14598a(11) =43815a(12) =131384a(13) =394213a(14) =1182456a(15) =3547551a(16) =10642110a(17) =31926873a(18) =95778990a(19) =287338599a(20) =862010924a(21) =2586037645a(22) =7758098316a(23) =23274309567a(24) =69822884886a(25) =209468698473a(26) =628405963974