Sets with a congruence property.

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =6a(5) =14a(6) =24a(7) =46a(8) =88a(9) =162a(10) =300a(11) =562a(12) =1056a(13) =1982a(14) =3742a(15) =7082a(16) =13438a(17) =25574a(18) =48768a(19) =93198a(20) =178480a(21) =342392a(22) =657918a(23) =1266202a(24) =2440318a(25) =4709374a(26) =9099504a(27) =17602322a(28) =34087010a(29) =66076414