Pair up the numbers.

Terms

a(0) =1a(1) =23a(2) =45a(3) =67a(4) =89a(5) =1011a(6) =1213a(7) =1415a(8) =1617a(9) =1819a(10) =2021a(11) =2223a(12) =2425a(13) =2627a(14) =2829a(15) =3031a(16) =3233a(17) =3435a(18) =3637a(19) =3839a(20) =4041a(21) =4243a(22) =4445a(23) =4647a(24) =4849a(25) =5051a(26) =5253a(27) =5455a(28) =5657a(29) =5859