Sierpinski tetrahedron or tetrix numbers: a(n) = 2*4^n + 2.

Terms

a(0) =4a(1) =10a(2) =34a(3) =130a(4) =514a(5) =2050a(6) =8194a(7) =32770a(8) =131074a(9) =524290a(10) =2097154a(11) =8388610a(12) =33554434a(13) =134217730a(14) =536870914a(15) =2147483650a(16) =8589934594a(17) =34359738370a(18) =137438953474a(19) =549755813890