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

Author

Patrick De Geest, May 15 1999

Keywords

• nonn
• base
• easy

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]

Examples

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

Links

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

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.

Programs

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

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 *)