A048439 Take the first n numbers written in base 7, concatenate them, then convert from base 7 to base 10.

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

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

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

Adjacent sequences: A048436 A048437 A048438 * A048440 A048441 A048442

Keyword

nonn,base,easy

Author

Patrick De Geest, May 15 1999

Status

approved