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A048436
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Take the first n numbers written in base 4, concatenate them, then convert from base 4 to base 10.
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19
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1, 6, 27, 436, 6981, 111702, 1787239, 28595832, 457533321, 7320533146, 117128530347, 1874056485564, 29984903769037, 479758460304606, 7676135364873711, 491272663351917520, 31441450454522721297, 2012252829089454163026
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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There is no prime among the first 5000 terms (emails from Kurt Foster, Oct 21 2015 and Oct 24 2015). When is the first prime? - N. J. A. Sloane, Oct 25 2015
There is no prime among the first 45000 terms. - Giovanni Resta, Jun 07 2018
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LINKS
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FORMULA
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EXAMPLE
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a(7): (1)(2)(3)(10)(11)(12)(13) = 12310111213_4 = 1787239.
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MATHEMATICA
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a[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 4], 4]; Array[a, 20] (* Vincenzo Librandi, Dec 30 2012 *)
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PROG
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(Magma) [n eq 1 select 1 else Self(n-1) * 4^(1+Ilog(4, n)) + n: n in [1..20]]; // Jason Kimberley, Nov 27 2012
(Python)
from functools import reduce
def A048436(n): return reduce(lambda i, j:(i<<(bool((m:=j.bit_length())&1)<<1)+(m&-2))+j, range(n+1)) # Chai Wah Wu, Feb 26 2023
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CROSSREFS
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Concatenation of first n numbers in other bases: 2: A047778, 3: A048435, 4: this sequence, 5: A048437, 6: A048438, 7: A048439, 8: A048440, 9: A048441, 10: A007908, 11: A048442, 12: A048443, 13: A048444, 14: A048445, 15: A048446, 16: A048447. - Dylan Hamilton, Aug 11 2010
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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