a(n) = Sum_{k=0..binomial(n,2)} (-1)^k*A152534(n,k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =6a(6) =10a(7) =23a(8) =47a(9) =110a(10) =246a(11) =617a(12) =1602a(13) =4035a(14) =11481a(15) =29927a(16) =95503a(17) =249926a(18) =871030a(19) =2316317a(20) =8879558a(21) =23674841a(22) =98329551a(23) =264329177a(24) =1191578522a(25) =3207278255a(26) =15543026747a(27) =42011308653a(28) =218668538441a(29) =591460307157