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 A060630 a(n) gives smallest number requiring n iterations of the map i -> A053392(i) to reach zero. 2

%I

%S 0,1,10,19,109,149,197,399,694,796,893,897,1167,1579,1596,1667,1790,

%T 1777,2859,1779,1778,1873,3679,5926,11289,9539,13551,4589,5960,12066,

%U 12265,19119,10927,12379,11742,65220,34038,40390,1110025,10100023

%N a(n) gives smallest number requiring n iterations of the map i -> A053392(i) to reach zero.

%C 24th and 26th terms are unknown, but a(25)=9539, a(27)=4589 and a(28)=5960.

%H Erich Friedman, <a href="https://erich-friedman.github.io/mathmagic/0200.html">Problem of the Month (Feb 2000)</a>

%F a(n)=10^(n-2)+9, for n=2, 3, 4 and for n > 40.

%e a(5)=149 because 149 -(1)-> 513 -(2)-> 64 -(3)-> 10 -(4)-> 1 -(5)-> 0. a(7)=399 because 399 -(1)-> 1218 -(2)-> 339 -(3)-> 612 -(4)-> 73 -(5)-> 10 -(6)-> 1 -(7)-> 0.

%Y Cf. A053392.

%K base,nonn

%O 0,3

%A _Jason Earls_, Apr 14 2001

%E More terms from Berend Jan van der Zwaag, Jun 23 2001

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Last modified April 18 05:11 EDT 2021. Contains 343072 sequences. (Running on oeis4.)