[seqfan] Re: Iterating sigma - 1
Richard Mathar
mathar at strw.leidenuniv.nl
Fri May 7 12:20:30 CEST 2010
rgw> From: "Robert G. Wilson v" <rgwv at rgwv.com>
rgw> Fri May 7 05:49:28 CEST 2010
rgw> To: "Sequence Fanatics Discussion list" <seqfan at list.seqfan.eu>
rgw> Subject: [seqfan] Re: Iterating sigma - 1
rgw> ...
rgw> You wish to submit a sequence of the least k such that the number of
rgw> iterations is n?
..
tdn> Good idea, but it is already in OEIS: A039656
Although this aspect is in A039656, the associated RECORDS transform
(index and value of new A039656 such that the value is larger than all
values at smaller indices)
2 0
4 2
9 5
121 6
301 7
441 11
468 13
3171 15
8373 17
13440 21
16641 23
16804 24
83161 25
100652 26
133200 29
367428 40
395640 42
459680 44
seems not to be in the OEIS.
RJM
In Maple 9:
A039655 := proc(n)
local x,a ;
x := n ;
a := 0 ;
while not isprime(x) do
x := numtheory[sigma](x)-1 ;
a := a+1 ;
end do:
a ;
end proc:
recsn := -1 ;
recsa := -1 ;
for n from 2 do
a := A039655(n) ;
if a > recsa then
recsn := n ;
recsa := a ;
printf("%d %d\n",recsn,recsa) ;
end if;
end do:
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