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A048436 Take the first n numbers written in base 4, concatenate them, then convert from base 4 to base 10. 19
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)
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

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Last modified March 28 13:25 EDT 2024. Contains 371254 sequences. (Running on oeis4.)