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A033175 n 3's followed by 1. 15
1, 31, 331, 3331, 33331, 333331, 3333331, 33333331, 333333331, 3333333331, 33333333331, 333333333331, 3333333333331, 33333333333331, 333333333333331, 3333333333333331, 33333333333333331, 333333333333333331, 3333333333333333331, 33333333333333333331 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
REFERENCES
F. Smarandache, Properties of numbers, University of Craiova, 1973.
LINKS
Eric Weisstein's World of Mathematics, 3
FORMULA
a(n) = (10^(n+1) - 7)/3.
a(n) = 10*a(n-1) + 21 (with a(0)=1). - Vincenzo Librandi, Nov 17 2010
G.f.: ( 1+20*x ) / ( (10*x-1)*(x-1) ). - R. J. Mathar, Aug 24 2011
MATHEMATICA
Table[FromDigits[PadLeft[{1}, n, 3]], {n, 20}] (* Harvey P. Dale, Feb 21 2013 *)
PROG
(PARI) a(n)=(10^(n+1)-7)/3 \\ Charles R Greathouse IV, Oct 07 2015
(GAP) List([0..20], n->(10^(n+1)-7)/3); # Muniru A Asiru, Oct 31 2018
(Python)
def a(n): return int('3'*n + '1')
print([a(n) for n in range(20)]) # Michael S. Branicky, Jan 31 2021
CROSSREFS
Cf. A051200.
Sequence in context: A029813 A138697 A186071 * A123568 A111675 A142495
KEYWORD
nonn,base,easy
AUTHOR
Jan Jensen (dorul(AT)post6.tele.dk)
STATUS
approved

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Last modified May 18 12:18 EDT 2024. Contains 372630 sequences. (Running on oeis4.)