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 A038395 Concatenation of the first n odd numbers in reverse order. 4
 1, 31, 531, 7531, 97531, 1197531, 131197531, 15131197531, 1715131197531, 191715131197531, 21191715131197531, 2321191715131197531, 252321191715131197531, 27252321191715131197531, 2927252321191715131197531, 312927252321191715131197531 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) starts with the digits of 2n-1. Indices of prime or probable prime terms are 1,2,37,62,409,...: see also A089922. - M. F. Hasler, Apr 13 2008 If n == 0 (mod 3), so is a(n). - Sergey Pavlov, Mar 29 2017 REFERENCES Mihaly Bencze [Beneze] and L. Tutescu, Some Notions and Questions in Number Theory, Sequence 3. LINKS Table of n, a(n) for n=1..16. Florentin Smarandache, Sequences of Numbers Involved in Unsolved Problems, arXiv:math/0604019 [math.GM], 2006. FORMULA a(n) = (2*n-1)*10^floor(1+log_10(a(n-1))) + a(n-1), with a(1)=1. - Paolo P. Lava, Jun 19 2008 MAPLE P:=proc(i) local a, n; a:=1; print(a); for n from 2 by 1 to i do a:=(2*n-1)*10^floor(evalf(1+log10(a), 100))+a ; print(a); od; end: P(100); # Paolo P. Lava, Jun 19 2008 MATHEMATICA Table[FromDigits[Flatten[IntegerDigits/@Join[Reverse[Range[1, n, 2]]]]], {n, 1, 29, 2}] (* Harvey P. Dale, Jun 02 2011 *) PROG (PARI) t=""; for( n=1, 10^3, ( t=eval( Str( 2*n-1, t))) & print(n" "t)) \\ M. F. Hasler, Apr 13 2008 (Python) def a(n): return int("".join(map(str, range(2*n-1, 0, -2)))) print([a(n) for n in range(1, 17)]) # Michael S. Branicky, Jan 31 2021 CROSSREFS Cf. A089922, A109837, A038394-A038399, A019518, A019519. Sequence in context: A316457 A278558 A022659 * A261620 A196492 A240420 Adjacent sequences: A038392 A038393 A038394 * A038396 A038397 A038398 KEYWORD nonn,base,easy AUTHOR M. I. Petrescu (mipetrescu(AT)yahoo.com) EXTENSIONS Edited and extended by M. F. Hasler, Apr 13 2008 Edited by T. D. Noe, Oct 30 2008 STATUS approved

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Last modified September 28 23:23 EDT 2023. Contains 365739 sequences. (Running on oeis4.)