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%I #46 Sep 08 2022 08:44:57
%S 1,9,66,466,3267,22875,1120882,54923226,2691238083,131870666077,
%T 6461662637784,316621469251428,15514451993319985,760208147672679279,
%U 37250199235961284686,1825259762562102949630,89437728365543044531887
%N Take the first n numbers written in base 7, concatenate them, then convert from base 7 to base 10.
%C The first two primes in this sequence occur for n = 10 (a(10) = 131870666077) and n = 37 (a(37) = 569432644200356239518976257368822195317881440478377541397) (email from Kurt Foster, Oct 24 2015). What is the next prime? - _N. J. A. Sloane_, Oct 25 2015
%C After a(37), there are no more primes through a(4000) = 2.2670...*10^14538. - _Jon E. Schoenfield_, Jan 19 2018
%H Vincenzo Librandi, <a href="/A048439/b048439.txt">Table of n, a(n) for n = 1..200</a>
%e a(8): (1)(2)(3)(4)(5)(6)(7)(10)(11) = 1234561011_7 = 54923226.
%t a[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 7], 7]; Array[a, 20] (* _Vincenzo Librandi_, Dec 30 2012 *)
%o (Magma) [n eq 1 select 1 else Self(n-1)*7^(1+Ilog(7, n))+n: n in [1..20]]; // _Vincenzo Librandi_, Dec 30 2012
%Y Cf. A014830.
%Y Concatenation of first n numbers in other bases: 2: A047778, 3: A048435, 4: A048436, 5: A048437, 6: A048438, 7: this sequence, 8: A048440, 9: A048441, 10: A007908, 11: A048442, 12: A048443, 13: A048444, 14: A048445, 15: A048446, 16: A048447.
%K nonn,base,easy
%O 1,2
%A _Patrick De Geest_, May 15 1999
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