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URL: https://oeis.org/A048435

⇱ A048435 - OEIS

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A048435
Take the first n numbers written in base 3, concatenate them, then convert from base 3 to base 10.
22
1, 5, 48, 436, 3929, 35367, 318310, 2864798, 77349555, 2088437995, 56387825876, 1522471298664, 41106725063941, 1109881576726421, 29966802571613382, 809103669433561330, 21845799074706155927, 589836575017066210047, 15925587525460787671288, 429990863187441267124796
OFFSET
1,2
COMMENTS
The first three primes in this sequence occur for n = 2 (a(2) = 5), n = 5 (a(5) = 3929), and n = 82 (a(82) = 1.1247...*10^140). - Kurt Foster, Oct 24 2015 [Comment added by N. J. A. Sloane, Oct 25 2015]
According to a comment made by Jeff Peltier following the "Most Wanted Prime" video, n = 2546 also gives a prime. See A360503. - N. J. A. Sloane, Feb 17 2023
LINKS
Brady Haran and N. J. A. Sloane, Most Wanted Prime, Numberphile video, December 2021.
EXAMPLE
a(6): (1)(2)(10)(11)(12)(20) = 1210111220_3 = 35367.
MATHEMATICA
If[STARTPOINT==1, n={}, n=Flatten[IntegerDigits[Range[STARTPOINT-1], 3]]]; Table[AppendTo[n, IntegerDigits[w, 3]]; n=Flatten[n]; FromDigits[n, 3], {w, STARTPOINT, ENDPOINT}] (* Dylan Hamilton, Aug 09-04 2010 *)
f[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 3], 3]; Array[f, 20] (* Vincenzo Librandi, Dec 30 2012 *)
PROG
(Magma) [n eq 1 select 1 else Self(n-1)*3^(1+Ilog(3, n))+n: n in [1..20]]; // Vincenzo Librandi, Dec 30 2012
CROSSREFS
Primes: A360503.
Concatenation of first n numbers in other bases: 2: A047778, 3: this sequence, 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: A048447.
Sequence in context: A247769 A389337 A116431 * A293102 A023999 A126224
KEYWORD
nonn,base,easy
AUTHOR
Patrick De Geest, May 15 1999
STATUS
approved