a(n) = 11 + floor(Sum_{j-1..n-1} a(j)/4).

Terms

a(0) =11a(1) =13a(2) =17a(3) =21a(4) =26a(5) =33a(6) =41a(7) =51a(8) =64a(9) =80a(10) =100a(11) =125a(12) =156a(13) =195a(14) =244a(15) =305a(16) =381a(17) =476a(18) =595a(19) =744a(20) =930a(21) =1163a(22) =1453a(23) =1817a(24) =2271a(25) =2839a(26) =3548a(27) =4435a(28) =5544a(29) =6930