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URL: https://oeis.org/A048439

⇱ A048439 - OEIS

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A048439
Take the first n numbers written in base 7, concatenate them, then convert from base 7 to base 10.
17
1, 9, 66, 466, 3267, 22875, 1120882, 54923226, 2691238083, 131870666077, 6461662637784, 316621469251428, 15514451993319985, 760208147672679279, 37250199235961284686, 1825259762562102949630, 89437728365543044531887, 4382448689911609182062481
OFFSET
1,2
COMMENTS
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
After a(37), there are no more primes through a(4000) = 2.2670...*10^14538. - Jon E. Schoenfield, Jan 19 2018
LINKS
EXAMPLE
a(8): (1)(2)(3)(4)(5)(6)(10)(11) = 1234561011_7 = 54923226.
MATHEMATICA
a[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 7], 7]; Array[a, 20] (* Vincenzo Librandi, Dec 30 2012 *)
PROG
(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
CROSSREFS
Cf. A014830.
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.
Sequence in context: A037607 A055148 A014830 * A134432 A098107 A226201
KEYWORD
nonn,base,easy
AUTHOR
Patrick De Geest, May 15 1999
STATUS
approved