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A038395
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Concatenation of the first n odd numbers in reverse order.
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4
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1, 31, 531, 7531, 97531, 1197531, 131197531, 15131197531, 1715131197531, 191715131197531, 21191715131197531, 2321191715131197531, 252321191715131197531, 27252321191715131197531, 2927252321191715131197531, 312927252321191715131197531
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OFFSET
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1,2
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COMMENTS
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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
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REFERENCES
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Mihaly Bencze [Beneze] and L. Tutescu, Some Notions and Questions in Number Theory, Sequence 3.
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LINKS
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Table of n, a(n) for n=1..16.
Florentin Smarandache, Sequences of Numbers Involved in Unsolved Problems, arXiv:math/0604019 [math.GM], 2006.
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FORMULA
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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
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MAPLE
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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
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MATHEMATICA
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Table[FromDigits[Flatten[IntegerDigits/@Join[Reverse[Range[1, n, 2]]]]], {n, 1, 29, 2}] (* Harvey P. Dale, Jun 02 2011 *)
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PROG
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(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
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CROSSREFS
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Cf. A089922, A109837, A038394-A038399, A019518, A019519.
Sequence in context: A316457 A278558 A022659 * A261620 A196492 A240420
Adjacent sequences: A038392 A038393 A038394 * A038396 A038397 A038398
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KEYWORD
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nonn,base,easy
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AUTHOR
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M. I. Petrescu (mipetrescu(AT)yahoo.com)
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EXTENSIONS
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Edited and extended by M. F. Hasler, Apr 13 2008
Edited by T. D. Noe, Oct 30 2008
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STATUS
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approved
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