Self-convolution of Pell numbers (A000129).

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =14a(5) =44a(6) =131a(7) =376a(8) =1052a(9) =2888a(10) =7813a(11) =20892a(12) =55338a(13) =145428a(14) =379655a(15) =985520a(16) =2545720a(17) =6547792a(18) =16777993a(19) =42847988a(20) =109099078a(21) =277040572a(22) =701794187a(23) =1773851304a(24) =4474555476a(25) =11266301976a(26) =28318897549a(27) =71070913036a(28) =178106093666a(29) =445740656420