Composite numbers whose prime factors contain no digits other than 1 and 4.

Terms

a(0) =121a(1) =451a(2) =1331a(3) =1681a(4) =4961a(5) =14641a(6) =18491a(7) =45221a(8) =48851a(9) =54571a(10) =68921a(11) =125521a(12) =158521a(13) =161051a(14) =168551a(15) =182081a(16) =203401a(17) =452551a(18) =455521a(19) =467851a(20) =485221a(21) =497431a(22) =537361a(23) =590851a(24) =600281a(25) =758131a(26) =1380731a(27) =1686781a(28) =1697851a(29) =1743731