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Pair up the numbers.
5

%I #43 Sep 08 2022 08:44:50

%S 1,23,45,67,89,1011,1213,1415,1617,1819,2021,2223,2425,2627,2829,3031,

%T 3233,3435,3637,3839,4041,4243,4445,4647,4849,5051,5253,5455,5657,

%U 5859,6061,6263,6465,6667,6869,7071,7273,7475,7677,7879,8081,8283,8485,8687,8889

%N Pair up the numbers.

%H Michel Marcus, <a href="/A030656/b030656.txt">Table of n, a(n) for n = 0..5000</a>

%t seq[n_] := FromDigits[Flatten[IntegerDigits /@ #]] & /@ Partition[Range[0, (n + 1)*2], 2];

%t seq[44] (* _Harvey P. Dale_, Jan 24 2012, edited by _Robert P. P. McKone_, Jan 23 2021 *)

%o (Magma) [Seqint(Intseq(n+1) cat Intseq(n)): n in [0..86 by 2]]; // _Bruno Berselli_, Jun 18 2011

%o (PARI) a(n)=eval(Str(2*n,2*n+1)) \\ _Charles R Greathouse IV_, Jul 21 2016

%o (Python)

%o def a(n): return int(str(2*n)+str(2*n+1))

%o print([a(n) for n in range(45)]) # _Michael S. Branicky_, Jan 23 2021

%Y Cf. A030655.

%Y Subsequence of A005408.

%K base,nonn,easy

%O 0,2

%A _Maghraoui Abdelkader_

%E More terms from _Erich Friedman_