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A091628
Concatenation of n 2's followed by 3.
6
23, 223, 2223, 22223, 222223, 2222223, 22222223, 222222223, 2222222223, 22222222223, 222222222223, 2222222222223, 22222222222223, 222222222222223, 2222222222222223, 22222222222222223, 222222222222222223
OFFSET
1,1
COMMENTS
Sequence arising in Farideh Firoozbakht's solution to Prime Puzzle 251; 23 is the only pointer prime (A089823) not containing the digit "1".
LINKS
Tanya Khovanova, Recursive Sequences
Carlos Rivera's Prime Puzzles and Problems Connection, Puzzle 251, Pointer primes
FORMULA
a(n) = (10^(n+1) - 1)/9*2 + 1.
a(n) = 10*a(n-1) - 7, with a(1)=23. - Vincenzo Librandi, Nov 16 2010
From Colin Barker, May 06 2012: (Start)
a(n) = 11*a(n-1) - 10*a(n-2).
G.f.: x*(23-30*x)/((1-x)*(1-10*x)). (End)
PROG
(Magma) [ n eq 1 select 23 else 10*Self(n-1)-7: n in [1..17] ];
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Enoch Haga, Jan 24 2004
EXTENSIONS
Edited and extended by Ray Chandler, Feb 07 2004
STATUS
approved