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URL: https://oeis.org/A048436

⇱ A048436 - OEIS

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A048436
Take the first n numbers written in base 4, concatenate them, then convert from base 4 to base 10.
20
1, 6, 27, 436, 6981, 111702, 1787239, 28595832, 457533321, 7320533146, 117128530347, 1874056485564, 29984903769037, 479758460304606, 7676135364873711, 491272663351917520, 31441450454522721297, 2012252829089454163026, 128784181061725066433683
OFFSET
1,2
COMMENTS
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
LINKS
FORMULA
a(n) = a(n-1) * 4^(1 + floor(log4(n))) + n. [Moved from A117640 by Jason Kimberley, Nov 27 2012]
EXAMPLE
a(7): (1)(2)(3)(10)(11)(12)(13) = 12310111213_4 = 1787239.
MATHEMATICA
a[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 4], 4]; Array[a, 20] (* Vincenzo Librandi, Dec 30 2012 *)
PROG
(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
CROSSREFS
Cf. A014825.
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
Sequence in context: A322233 A164985 A367884 * A276412 A006174 A064810
KEYWORD
nonn,base,easy
AUTHOR
Patrick De Geest, May 15 1999
STATUS
approved