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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 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..17.

Tanya Khovanova, Recursive Sequences

Carlos Rivera's Prime Puzzles and Problems Connection, Puzzle 251, Pointer primes

Index entries for linear recurrences with constant coefficients, signature (11,-10).

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

Cf. A089823, A091629, A091630, A091631, A091632.

Sequence in context: A038514 A244766 A125386 * A126544 A272796 A285552

Adjacent sequences:  A091625 A091626 A091627 * A091629 A091630 A091631

KEYWORD

base,easy,nonn

AUTHOR

Enoch Haga, Jan 24 2004

EXTENSIONS

Edited and extended by Ray Chandler, Feb 07 2004

STATUS

approved

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Last modified November 16 00:11 EST 2018. Contains 317252 sequences. (Running on oeis4.)