A225813 - OEIS

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A225813

a(n) = (10^n)^2 + 7(10^n) + 1.

9, 171, 10701, 1007001, 100070001, 10000700001, 1000007000001, 100000070000001, 10000000700000001, 1000000007000000001, 100000000070000000001, 10000000000700000000001, 1000000000007000000000001, 100000000000070000000000001, 10000000000000700000000000001

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OFFSET

0,1

COMMENTS

This is an instance of (10^n)^2 + x(10^n) + 1 which umbrellas A066138, A033934, A171375, A171410, A171461, A171513 and A171553 which all produce palindromes of the form 1...x...1 when n <> 0.

LINKS

Colin Barker, Table of n, a(n) for n = 0..499

Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).

FORMULA

a(n) = 111*a(n-1)-1110*a(n-2)+1000*a(n-3). - Colin Barker, Apr 27 2015

G.f.: -9*(190*x^2-92*x+1) / ((x-1)*(10*x-1)*(100*x-1)). - Colin Barker, Apr 27 2015

MAPLE

A225813:=n->(10^n)^2 + 7*(10^n) + 1: seq(A225813(n), n=0..20); # Wesley Ivan Hurt, Apr 08 2017

MATHEMATICA

Table[(10^n)^2 + 7*(10^n) + 1, {n, 0, 20}] (* T. D. Noe, Aug 12 2013 *)

LinearRecurrence[{111, -1110, 1000}, {9, 171, 10701}, 20] (* Harvey P. Dale, Apr 12 2020 *)

PROG

(PARI) Vec(-9*(190*x^2-92*x+1)/((x-1)*(10*x-1)*(100*x-1)) + O(x^100)) \\ Colin Barker, Apr 27 2015

CROSSREFS

Sequence in context: A049212 A266856 A141441 * A357348 A357345 A336728

Adjacent sequences: A225810 A225811 A225812 * A225814 A225815 A225816

KEYWORD

nonn,easy

AUTHOR

Lance J. Weingartz, Jul 29 2013

STATUS

approved