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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
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
Sequence in context: A316457 A278558 A022659 * A261620 A196492 A240420
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.)