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A218123
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Denominators of terms of the sequence {c(n)} defined in A218121.
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2
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1, 2, 2, 2, 2, 3, 3, 3, 5, 5, 5, 7, 7, 7, 7, 7, 7, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 17, 17, 17, 17, 17, 17, 19, 19, 19, 19, 19, 19, 19, 23, 23, 23, 23, 23, 23, 23, 23, 29, 29, 29, 29, 31, 31, 31, 31, 31, 31, 31, 31, 31, 37, 37, 37, 37, 37, 37, 41, 41, 41, 41, 43, 43, 43, 43, 43, 43, 43, 47, 47
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OFFSET
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1,2
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COMMENTS
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It is easy to see that every prime is in the sequence.
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LINKS
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Table of n, a(n) for n=1..80.
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MAPLE
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ispfree := proc(a, b)
local alow ;
alow := floor(a);
if nextprime(alow) < b then
false;
else
true;
end if;
end proc:
A218121c := proc(n)
option remember;
local k ;
if n = 1 then
return 1;
elif n = 2 then
return 5/2 ;
else
if ispfree(ithprime(n)/procname(n-1), ithprime(n+1)/procname(n-1)) then
return procname(n-1) ;
end if ;
for k from n by -1 do
if ispfree( ithprime(n)*ithprime(k)/ithprime(n+1), ithprime(k) )
and ithprime(n+1)/ithprime(k) > procname(n-1) then
return ithprime(n+1)/ithprime(k) ;
end if;
end do:
end if;
end proc:
A218123 := proc(n)
denom(A218121c(n)) ;
end proc: # R. J. Mathar, Dec 02 2012
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CROSSREFS
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Cf. A218121, A217871, A217689, A217691, A217833, A217884.
Sequence in context: A029084 A032229 A024366 * A288157 A333701 A140682
Adjacent sequences: A218120 A218121 A218122 * A218124 A218125 A218126
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KEYWORD
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nonn,frac
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AUTHOR
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Vladimir Shevelev, Oct 21 2012
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STATUS
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approved
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