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 A272067 a(n) = (10^n-1)^4. 5
 0, 6561, 96059601, 996005996001, 9996000599960001, 99996000059999600001, 999996000005999996000001, 9999996000000599999960000001, 99999996000000059999999600000001, 999999996000000005999999996000000001, 9999999996000000000599999999960000000001, 99999999996000000000059999999999600000000001 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The sum of the digits of a(n) is divisible by 18. For example, 9^4 = 6561 and 6 + 5 + 6 + 1 = 18 * 1. Number of 9 in a(n) is 2*n-2 for n > 0. - Seiichi Manyama, Sep 18 2018 LINKS FORMULA a(n) = A059988(n)^2 = A002283(n)^4. From Ilya Gutkovskiy, Apr 19 2016: (Start) O.g.f.: 6561*x*(1 + 100*x)*(1 + 3430*x + 10000*x^2)/((1 - x)*(1 - 10*x)*(1 - 100*x)*(1 - 1000*x)*(1 - 10000*x)). E.g.f.: (1 - 4*exp(9*x) + 6*exp(99*x) - 4*exp(999*x) + exp(9999*x))*exp(x). (End) EXAMPLE From Seiichi Manyama, Sep 18 2018: (Start) n| a(n) can be divided into 4 parts for n > 1. -+-------------------------------------------- 1|        65        61 2|   9   605   9   601 3|  99  6005  99  6001 4| 999 60005 999 60001 (End) MAPLE A272067:=n->(10^n-1)^4: seq(A272067(n), n=0..15); # Wesley Ivan Hurt, Apr 19 2016 MATHEMATICA (10^Range[0, 10] - 1)^4 (* Wesley Ivan Hurt, Apr 19 2016 *) PROG (Ruby) (0..n).each{|i| p ('9' * i).to_i ** 4} (PARI) a(n) = (10^n-1)^4; \\ Michel Marcus, Apr 19 2016 (MAGMA) [(10^n-1)^4 : n in [0..10]]; // Wesley Ivan Hurt, Apr 19 2016 CROSSREFS Cf. A002283, A059988, A272066, A272068, A319358. Sequence in context: A016844 A016892 A016952 * A017024 A017108 A013853 Adjacent sequences:  A272064 A272065 A272066 * A272068 A272069 A272070 KEYWORD nonn,easy AUTHOR Seiichi Manyama, Apr 19 2016 STATUS approved

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Last modified January 17 09:32 EST 2020. Contains 330949 sequences. (Running on oeis4.)