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 A048436 Take the first n numbers written in base 4, concatenate them, then convert from base 4 to base 10. 18
 1, 6, 27, 436, 6981, 111702, 1787239, 28595832, 457533321, 7320533146, 117128530347, 1874056485564, 29984903769037, 479758460304606, 7676135364873711, 491272663351917520, 31441450454522721297, 2012252829089454163026 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There is no prime among the first 5000 terms (emails from Kurt Foster, Oct 21 2015 and Oct 24 2015). When is the first prime? - N. J. A. Sloane, Oct 25 2015 There is no prime among the first 45000 terms. - Giovanni Resta, Jun 07 2018 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..200 FORMULA a(n) = a(n-1) * 4^(1 + floor(log4(n))) + n. [Moved from A117640 by Jason Kimberley, Nov 27 2012] EXAMPLE a(7): (1)(2)(3)(10)(11)(12)(13) = 12310111213_4 = 1787239. MATHEMATICA If[STARTPOINT==1, n={}, n=Flatten[IntegerDigits[Range[STARTPOINT-1], 4]]]; Table[AppendTo[n, IntegerDigits[w, 4]]; n=Flatten[n]; FromDigits[n, 4], {w, STARTPOINT, ENDPOINT}] (* Dylan Hamilton, Aug 04 2010 *) f[n_]:= FromDigits[Flatten@IntegerDigits[Range@n, 4], 4]; Array[f, 20] (* Vincenzo Librandi, Dec 30 2012 *) PROG (MAGMA) [n eq 1 select 1 else Self(n-1) * 4^(1+Ilog(4, n)) + n: n in [1..20]]; // Jason Kimberley, Nov 27 2012 CROSSREFS Cf. A014825. Concatenation of first n numbers in other bases: 2: A047778, 3: A048435, 4: this sequence, 5: A048437, 6: A048438, 7: A048439, 8: A048440, 9: A048441, 10: A007908, 11: A048442, 12: A048443, 13: A048444, 14: A048445, 15: A048446, 16: A048447. - Dylan Hamilton, Aug 11 2010 Sequence in context: A290802 A322233 A164985 * A276412 A006174 A064810 Adjacent sequences:  A048433 A048434 A048435 * A048437 A048438 A048439 KEYWORD nonn,base,easy AUTHOR Patrick De Geest, May 15 1999 STATUS approved

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Last modified February 18 00:37 EST 2020. Contains 332006 sequences. (Running on oeis4.)