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A047901 a(1) = 9; a(n+1) = a(n) * sum of decimal digits of a(n).

%I A047901 #14 May 22 2025 10:21:34
%S A047901 9,81,729,13122,118098,3188646,114791256,4132485216,148769467776,
%T A047901 10711401679872,578415690713088,41645929731342336,2998506940656648192,
%U A047901 296852187125008171008,24045027157125661851648,2164052444141309566648320
%N A047901 a(1) = 9; a(n+1) = a(n) * sum of decimal digits of a(n).
%H A047901 Reinhard Zumkeller, <a href="/A047901/b047901.txt">Table of n, a(n) for n = 1..250</a>
%F A047901 a(n+1) = A057147(a(n)). - _Reinhard Zumkeller_, Mar 19 2014
%t A047901 NestList[# Total[IntegerDigits[#]]&,9,20] (* _Harvey P. Dale_, Feb 07 2022 *)
%o A047901 (Haskell)
%o A047901 a047901 n = a047901_list !! (n-1)
%o A047901 a047901_list = iterate a057147 9  -- _Reinhard Zumkeller_, Mar 19 2014
%o A047901 (Python)
%o A047901 A047901_list, l = [9], 9
%o A047901 for _ in range(10**2):
%o A047901     l *= sum(int(d) for d in str(l))
%o A047901     A047901_list.append(l) # _Chai Wah Wu_, Jan 04 2015
%Y A047901 Cf. A047892 (start=2), A047912 (start=3), A047897 (start=5), A047898 (start=6), A047899 (start=7), A047900 (start=8), A047902 (start=11).
%K A047901 easy,nonn,base
%O A047901 1,1
%A A047901 Miklos SZABO (mike(AT)ludens.elte.hu)
%E A047901 Edited by _Charles R Greathouse IV_, Aug 02 2010