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Odd numbers taking exactly 21 steps to reach 15 in A086793.
3

%I #7 Apr 03 2018 15:13:32

%S 628425,824175,1340325,1422135,1495725,1729665,1845585,1853775,

%T 1916145,2001825,2015685,2040675,2045505,2091375,2165625,2220435,

%U 2226609,2264535,2333925,2360085,2365965,2379465,2465925,2474955,2499255,2511495

%N Odd numbers taking exactly 21 steps to reach 15 in A086793.

%C Most terms are multiples of 5. In the first 130 terms, there only 19 non-multiples of 5: 2226609, 2556477, 3252249, 3496779, 3638439, 4060287, 4779621, 4821453, 5146713, 5313231, 5365899, 5504499, 5578419, 5738733, 5785857, 5845749, 6189183, 6222447, 6236769.

%H Robert Israel, <a href="/A119398/b119398.txt">Table of n, a(n) for n = 1..500</a>

%p f:= proc(n) option remember; local t;

%p if kernelopts(level) > 460 then return FAIL fi;

%p t:= add(convert(convert(d,base,10),`+`),d=numtheory:-divisors(n));

%p 1+procname(t)

%p end proc:

%p f(15):= 0:

%p f(1):= FAIL:

%p Res:= NULL: count:= 0:

%p for n from 1 by 2 while count < 100 do

%p if f(n) = 21 then Res:= Res, n; count:= count+1 fi;

%p od:

%p Res; # _Robert Israel_, Apr 03 2018

%Y Cf. A086793, A119396-A119415.

%K base,nonn

%O 1,1

%A _Zak Seidov_, May 18 2006

%E a(1)=628425 inserted by _Robert Israel_, Apr 03 2018