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 A332119 a(n) = (10^(2n+1)-1)/9 + 8*10^n. 13
 9, 191, 11911, 1119111, 111191111, 11111911111, 1111119111111, 111111191111111, 11111111911111111, 1111111119111111111, 111111111191111111111, 11111111111911111111111, 1111111111119111111111111, 111111111111191111111111111, 11111111111111911111111111111, 1111111111111119111111111111111 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS See A107649 = {1, 4, 26, 187, 226, 874, ...} for the indices of primes. LINKS Brady Haran and Simon Pampena, Glitch Primes and Cyclops Numbers, Numberphile video (2015). Patrick De Geest, Palindromic Wing Primes: (1)9(1), updated: June 25, 2017. Makoto Kamada, Factorization of 11...11911...11, updated Dec 11 2018. Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000). FORMULA a(n) = A138148(n) + 9*10^n = A002275(2n+1) + 8*10^n. G.f.: (9 - 808*x + 700*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 A332119 := n -> (10^(2*n+1)-1)/9+8*10^n; MATHEMATICA Array[(10^(2 # + 1)-1)/9 + 8*10^# &, 15, 0] PROG (PARI) apply( {A332119(n)=10^(n*2+1)\9+8*10^n}, [0..15]) (Python) def A332119(n): return 10**(n*2+1)//9+8*10**n CROSSREFS Cf. (A077795-1)/2 = A107649: indices of primes. Cf. A002275 (repunits R_n = (10^n-1)/9), A011557 (10^n). Cf. A138148 (cyclops numbers with binary digits), A002113 (palindromes). Cf. A332129 .. A332189 (variants with different repeated digit 2, ..., 8). Cf. A332112 .. A332118 (variants with different middle digit 2, ..., 8). Sequence in context: A119291 A113269 A307387 * A261826 A184688 A189178 Adjacent sequences:  A332116 A332117 A332118 * A332120 A332121 A332122 KEYWORD nonn,base,easy AUTHOR M. F. Hasler, Feb 09 2020 STATUS approved

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Last modified August 19 03:31 EDT 2022. Contains 356216 sequences. (Running on oeis4.)