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A048447 Take the first n numbers written in base 16, concatenate them, then convert from base 16 to base 10.

%I A048447 #28 Jun 13 2025 10:49:55
%S A048447 1,18,291,4660,74565,1193046,19088743,305419896,4886718345,
%T A048447 78187493530,1250999896491,20015998343868,320255973501901,
%U A048447 5124095576030430,81985529216486895,20988295479420645136,5373003642731685154833,1375488932539311399637266,352125166730063718307140115
%N A048447 Take the first n numbers written in base 16, concatenate them, then convert from base 16 to base 10.
%H A048447 Vincenzo Librandi, <a href="/A048447/b048447.txt">Table of n, a(n) for n = 1..200</a>
%e A048447 a(16) = (1)(2)(3)(4)(5)(6)(7)(8)(9)(A)(B)(C)(D)(E)(F)(10) = 123456789ABCDEF10_16 = 20988295479420645136.
%t A048447 If[STARTPOINT==1, n={}, n=Flatten[IntegerDigits[Range[STARTPOINT-1], 16]]]; Table[AppendTo[n, IntegerDigits[w, 16]]; n=Flatten[n]; FromDigits[n, 16], {w, STARTPOINT, ENDPOINT}] (* _Dylan Hamilton_, Aug 11 2010 *)
%t A048447 f[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 16], 16]; Array[f, 20] (* _Vincenzo Librandi_, Dec 30 2012 *)
%o A048447 (Magma) [n eq 1 select 1 else Self(n-1)*16^(1+Ilog(16, n))+n: n in [1..20]]; // _Vincenzo Librandi_, Dec 30 2012
%o A048447 (Python)
%o A048447 from functools import reduce
%o A048447 def A048447(n): return reduce(lambda i,j:(i<<(bool((m:=j.bit_length())&3)<<2)+(m&-4))+j,range(n+1)) # _Chai Wah Wu_, Feb 26 2023
%Y A048447 Cf. A014899.
%Y A048447 Concatenation of first n numbers in other bases: 2: A047778, 3: A048435, 4: A048436, 5: A048437, 6: A048438, 7: A048439, 8: A048440, 9: A048441, 10: A007908, 11: A048442, 12: A048443, 13: A048444, 14: A048445, 15: A048446, 16: this sequence.
%K A048447 nonn,base,easy
%O A048447 1,2
%A A048447 _Patrick De Geest_, May 15 1999