Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #54 Apr 28 2024 09:49:27
%S 1,9,66,466,3267,22875,1120882,54923226,2691238083,131870666077,
%T 6461662637784,316621469251428,15514451993319985,760208147672679279,
%U 37250199235961284686,1825259762562102949630,89437728365543044531887,4382448689911609182062481
%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)(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