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 A106001 Start S with 1; extend S with a(n) such that a(n) is the smallest unused integer so far that ends with the a(n)-th digit of S. 2
 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 21, 12, 31, 41, 22, 13, 51, 14, 61, 32, 42, 71, 23, 15, 81, 91, 24, 16, 101, 33, 52, 34, 62, 17, 111, 72, 43, 121, 25, 18, 131, 19, 141, 82, 44, 151, 26, 161, 10, 171, 53, 63, 35, 92, 73, 54, 36, 102, 181, 27, 191, 201, 211, 37, 112, 64 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This is a permutation of the natural numbers as, in building the sequence, we always chose the smallest integer not yet present in it. The inverse is A252781. Eric Angelini, Jan 16 2015 LINKS Paul Tek, Table of n, a(n) for n = 1..10000 Éric Angelini, The a(n)th term of S ends with the a(n)th digit of S, SeqFan list, Jan 15 2015. Paul Tek, PERL program for this sequence EXAMPLE Last digits are: (1), (2), (3), (4), (5), (6), (7), (8), (9), 1(1), 2(1), 1(2), 3(1), 4(1), 2(2), 1(3), 5(1), 1(4), 6(1), 3(2), 4(2),... which form (1), (2), (3), (4), (5), (6), (7), (8), (9), (1), (1), (2), (1), (1), (2), (3), (1), (4), (1), (2), (2)... then 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 1, 2, 1, 1, 2, 3, 1, 4, 1, 2, 2,... which can be seen as 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 21, 12, 31, 41, 22,... thus the starting sequence. PROG (Haskell) import Data.List (delete) a250310 n = a250310_list !! (n-1) a250310_list = [1..9] ++ [11] ++ f ([0..9] ++ [1, 1]) 11 (10 : [12..])     where f ss i zs = g zs where         g (x:xs) = if ss !! i /= mod x 10             then g xs             else x : f (ss ++ map (read . return) (show x))                 (i + 1) (delete x zs) -- Reinhard Zumkeller, Jan 16 2015 CROSSREFS Cf. A010879, A252781 (inverse), A126968 Sequence in context: A267771 A275513 A038724 * A161390 A096106 A076641 Adjacent sequences:  A105998 A105999 A106000 * A106002 A106003 A106004 KEYWORD base,easy,nonn,look AUTHOR Eric Angelini, Apr 25 2005, revised Dec 06 2007 EXTENSIONS Data corrected by Paul Tek, Aug 11 2013 STATUS approved

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Last modified November 15 07:25 EST 2018. Contains 317225 sequences. (Running on oeis4.)