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 A178630 a(n) = 18 * ((10^n - 1)/9)^2. 13
 18, 2178, 221778, 22217778, 2222177778, 222221777778, 22222217777778, 2222222177777778, 222222221777777778, 22222222217777777778, 2222222222177777777778, 222222222221777777777778 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000). FORMULA a(n) = 18*A002477(n) = A002283(n)*A002276(n). a(n)=((A002276(n-1)*10+1)*10^(n-1)+A002281(n-1))*10+8. G.f.: 18*x*(1 + 10*x)/((1 - x)*(1 - 10*x)*(1 - 100*x)). - Ilya Gutkovskiy, Feb 24 2017 EXAMPLE n=1: ..................... 18 = 9 * 2; n=2: ................... 2178 = 99 * 22; n=3: ................. 221778 = 999 * 222; n=4: ............... 22217778 = 9999 * 2222; n=5: ............. 2222177778 = 99999 * 22222; n=6: ........... 222221777778 = 999999 * 222222; n=7: ......... 22222217777778 = 9999999 * 2222222; n=8: ....... 2222222177777778 = 99999999 * 22222222; n=9: ..... 222222221777777778 = 999999999 * 222222222. PROG (MAGMA) [18*((10^n - 1)/9)^2: n in [1..50]]; // Vincenzo Librandi, Dec 28 2010 (PARI) a(n)=18*(10^n\9)^2 \\ Charles R Greathouse IV, Aug 21 2011 CROSSREFS Cf. A075412, A178631, A075415, A178632, A178633, A178634, A178635, A059988. Sequence in context: A296614 A230818 A276017 * A136834 A279296 A299696 Adjacent sequences:  A178627 A178628 A178629 * A178631 A178632 A178633 KEYWORD nonn,easy AUTHOR Reinhard Zumkeller, May 31 2010 STATUS approved

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Last modified October 21 18:11 EDT 2018. Contains 316427 sequences. (Running on oeis4.)