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A332124 a(n) = 2*(10^(2n+1)-1)/9 + 2*10^n. 3
4, 242, 22422, 2224222, 222242222, 22222422222, 2222224222222, 222222242222222, 22222222422222222, 2222222224222222222, 222222222242222222222, 22222222222422222222222, 2222222222224222222222222, 222222222222242222222222222, 22222222222222422222222222222, 2222222222222224222222222222222 (list; graph; refs; listen; history; text; internal format)
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) + 4*10^n = A002276(2n+1) + 2*10^n = 2*A332112(n).

G.f.: (4 - 202*x)/((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

A332124 := n -> 2*((10^(2*n+1)-1)/9+10^n);

MATHEMATICA

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

PROG

(PARI) apply( {A332124(n)=(10^(n*2+1)\9+10^n)*2}, [0..15])

(Python) def A332124(n): return (10**(n*2+1)//9+10**n)*2

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. A332114 .. A332194 (variants with different repeated digit 1, ..., 9).

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

Sequence in context: A137342 A152793 A042769 * A091792 A300595 A320418

Adjacent sequences:  A332120 A332121 A332123 * A332125 A332126 A332127

KEYWORD

nonn,base,easy

AUTHOR

M. F. Hasler, Feb 09 2020

STATUS

approved

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Last modified August 4 13:49 EDT 2020. Contains 336201 sequences. (Running on oeis4.)