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A048435 Take the first n numbers written in base 3, concatenate them, then convert from base 3 to base 10.

%I A048435 #39 Jun 13 2025 10:49:14
%S A048435 1,5,48,436,3929,35367,318310,2864798,77349555,2088437995,56387825876,
%T A048435 1522471298664,41106725063941,1109881576726421,29966802571613382,
%U A048435 809103669433561330,21845799074706155927,589836575017066210047,15925587525460787671288,429990863187441267124796
%N A048435 Take the first n numbers written in base 3, concatenate them, then convert from base 3 to base 10.
%C A048435 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]
%C A048435 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
%H A048435 Vincenzo Librandi, <a href="/A048435/b048435.txt">Table of n, a(n) for n = 1..200</a>
%H A048435 Brady Haran and N. J. A. Sloane, <a href="https://www.youtube.com/watch?v=vKlVNFOHJ9I">Most Wanted Prime</a>, Numberphile video, December 2021.
%H A048435 <a href="/index/Mo#MWP">Index entries for sequences related to Most Wanted Primes video</a>
%e A048435 a(6): (1)(2)(10)(11)(12)(20) = 1210111220_3 = 35367.
%t A048435 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 *)
%t A048435 f[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 3], 3]; Array[f, 20] (* _Vincenzo Librandi_, Dec 30 2012 *)
%o A048435 (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
%Y A048435 Primes: A360503.
%Y A048435 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.
%K A048435 nonn,base,easy
%O A048435 1,2
%A A048435 _Patrick De Geest_, May 15 1999