A332187 a(n) = 8*(10^(2n+1)-1)/9 - 10^n.

7, 878, 88788, 8887888, 888878888, 88888788888, 8888887888888, 888888878888888, 88888888788888888, 8888888887888888888, 888888888878888888888, 88888888888788888888888, 8888888888887888888888888, 888888888888878888888888888, 88888888888888788888888888888, 8888888888888887888888888888888

Offset

0,1

Links

Table of n, a(n) for n=0..15.

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

Formula

a(n) = 8*A138148(n) + 7*10^n = A002282(2n+1) - 10^n.

G.f.: (7 + 101*x - 900*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.

Maple

A332187 := n -> 8*(10^(2*n+1)-1)/9-10^n;

Mathematica

Array[8 (10^(2 # + 1)-1)/9 - 10^# &, 15, 0]

Prog

(PARI) apply( {A332187(n)=10^(n*2+1)\9*8-10^n}, [0..15])
(Python) def A332187(n): return 10**(n*2+1)//9*8-10**n

Crossrefs

Cf. (A077776-1)/2 = A183190: indices of primes.

Cf. A002275 (repunits R_n = (10^n-1)/9), A002282 (8*R_n), A011557 (10^n).

Cf. A138148 (cyclops numbers with binary digits only), A002113 (palindromes).

Cf. A332117 .. A332197 (variants with different "wing" digit 1, ..., 9).

Cf. A332180 .. A332189 (variants with different middle digit 0, ..., 9).

Sequence in context: A308296 A193342 A298301 * A093171 A330295 A177908

Adjacent sequences: A332184 A332185 A332186 * A332188 A332189 A332190

Keyword

nonn,base,easy

Author

M. F. Hasler, Feb 08 2020

Status

approved