

A048439


Take the first n numbers written in base 7, concatenate them, then convert from base 7 to base 10.


16



1, 9, 66, 466, 3267, 22875, 1120882, 54923226, 2691238083, 131870666077, 6461662637784, 316621469251428, 15514451993319985, 760208147672679279, 37250199235961284686, 1825259762562102949630, 89437728365543044531887
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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

Vincenzo Librandi, Table of n, a(n) for n = 1..200


EXAMPLE

a(8): (1)(2)(3)(4)(5)(6)(7)(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(n1)*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
Adjacent sequences: A048436 A048437 A048438 * A048440 A048441 A048442


KEYWORD

nonn,base,easy


AUTHOR

Patrick De Geest, May 15 1999


STATUS

approved



