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%I #23 Apr 19 2023 17:47:25
%S 1,12,123,12310,1231011,123101112,12310111213,1231011121320,
%T 123101112132021,12310111213202122,1231011121320212223,
%U 123101112132021222330,12310111213202122233031
%N Concatenation of first n numbers in base 4.
%C Concatenation of the first n terms of A007090.
%C Base-4 analog of A058935.
%H N. J. A. Sloane, <a href="/A117640/b117640.txt">Table of n, a(n) for n = 1..35</a>
%t Table[FromDigits[Flatten[Table[IntegerDigits[n,4],{n,k}]]],{k,15}] (* _Harvey P. Dale_, Jan 18 2023 *)
%o (Python)
%o from gmpy2 import digits
%o def A117640(n): return int(''.join(digits(n,4) for n in range(1,n+1))) # _Chai Wah Wu_, Apr 19 2023
%Y Cf. A030373, A048436.
%Y Other bases: A058935 (2), A360502 (3), A007908 (10).
%K base,easy,nonn
%O 1,2
%A _Jonathan Vos Post_, Apr 27 2006
%E Edited by _Jason Kimberley_, Nov 27 2012
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