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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 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.)