A048437 Take the first n numbers written in base 5, concatenate them, then convert from base 5 to base 10.

1, 7, 38, 194, 4855, 121381, 3034532, 75863308, 1896582709, 47414567735, 1185364193386, 29634104834662, 740852620866563, 18521315521664089, 463032888041602240, 11575822201040056016, 289395555026001400417, 7234888875650035010443, 180872221891250875261094

Offset

1,2

Comments

The first three primes in this sequence occur for n = 2 (a(2) = 7), n = 113 (a(113) = 7.4484...*10^216), n = 162 (a(162) = 1.5188...*10^346). - Kurt Foster, Oct 24 2015 [Comment added by N. J. A. Sloane, Oct 25 2015]

Links

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

Example

a(7) = 1 2 3 4 10 11 12 = 3034532_10.

Mathematica

If[STARTPOINT==1, n={}, n=Flatten[IntegerDigits[Range[STARTPOINT-1], 5]]]; Table[AppendTo[n, IntegerDigits[w, 5]]; n=Flatten[n]; FromDigits[n, 5], {w, STARTPOINT, ENDPOINT}] (* Dylan Hamilton, Aug 11 2010 *)
f[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 5], 5]; Array[f, 20] (* Vincenzo Librandi, Dec 30 2012 *)

Prog

(Magma) [n eq 1 select 1 else Self(n-1)*5^(1+Ilog(5, n))+n: n in [1..20]]; // Vincenzo Librandi, Dec 30 2012

Crossrefs

Cf. A014827.

Concatenation of first n numbers in other bases: 2: A047778, 3: A048435, 4: A048436, 5: this sequence, 6: A048438, 7: A048439, 8: A048440, 9: A048441, 10: A007908, 11: A048442, 12: A048443, 13: A048444, 14: A048445, 15: A048446, 16: A048447.

Sequence in context: A055146 A014827 A141845 * A099461 A391176 A104553

Adjacent sequences: A048434 A048435 A048436 * A048438 A048439 A048440

Keyword

nonn,base,easy

Author

Patrick De Geest, May 15 1999

Status

approved