A332197 a(n) = 10^(2n+1) - 1 - 2*10^n.
7, 979, 99799, 9997999, 999979999, 99999799999, 9999997999999, 999999979999999, 99999999799999999, 9999999997999999999, 999999999979999999999, 99999999999799999999999, 9999999999997999999999999, 999999999999979999999999999, 99999999999999799999999999999, 9999999999999997999999999999999
Offset: 0
Links
- Patrick De Geest, Palindromic Wing Primes: (9)7(9), updated June 25, 2017.
- Makoto Kamada, Factorization of 99...99799...99, updated Dec 11 2018.
- Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).
Crossrefs
Programs
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Maple
A332197 := n -> 10^(n*2+1)-1-2*10^n;
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Mathematica
Array[ 10^(2 # + 1) -1 -2*10^# &, 15, 0] Table[FromDigits[Join[PadRight[{},n,9],{7},PadRight[{},n,9]]],{n,0,20}] (* or *) LinearRecurrence[{111,-1110,1000},{7,979,99799},20] (* Harvey P. Dale, Mar 03 2023 *)
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PARI
apply( {A332197(n)=10^(n*2+1)-1-2*10^n}, [0..15])
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Python
def A332197(n): return 10**(n*2+1)-1-2*10^n
Formula
a(n) = 9*A138148(n) + 7*10^n.
G.f.: (7 + 202*x - 1100*x^2)/((1 - x)*(1 - 10*x)*(1 - 100*x)).
a(n) = 111*a(n-1) - 1110*a(n-2) + 1000*a(n-3) for n > 2.
Comments