A332127 a(n) = 2*(10^(2n+1)-1)/9 + 5*10^n.

7, 272, 22722, 2227222, 222272222, 22222722222, 2222227222222, 222222272222222, 22222222722222222, 2222222227222222222, 222222222272222222222, 22222222222722222222222, 2222222222227222222222222, 222222222222272222222222222, 22222222222222722222222222222, 2222222222222227222222222222222

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) = 2*A138148(n) + 7*10^n = A002276(2n+1) + 5*10^n.

G.f.: (7 - 505*x + 300*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

A332127 := n -> 2*(10^(2*n+1)-1)/9+5*10^n;

Mathematica

Array[2 (10^(2 # + 1)-1)/9 + 5*10^# &, 15, 0]

Prog

(PARI) apply( {A332127(n)=10^(n*2+1)\9*2+5*10^n}, [0..15])
(Python) def A332127(n): return 10**(n*2+1)//9*2+5*10**n

Crossrefs

Cf. A002275 (repunits R_n = (10^n-1)/9), A002276 (2*R_n), A011557 (10^n).

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

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

Cf. A332120 .. A332129 (variants with different middle digit 0, ..., 9).

Sequence in context: A100465 A140031 A066413 * A222942 A289634 A065581

Adjacent sequences: A332124 A332125 A332126 * A332128 A332129 A332130

Keyword

nonn,base,easy

Author

M. F. Hasler, Feb 09 2020

Status

approved