OFFSET
1,1
COMMENTS
a(16) > 4*10^10. - Martin Fuller, Jan 17 2006
Apparently, 4*a(n)+2 is the least number k such that k-2 and k+2 have exactly n+2 prime factors, counted with multiplicity. - Hugo Pfoertner, Apr 02 2024
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 135, p. 46, Ellipses, Paris 2008.
EXAMPLE
MAPLE
f:= proc(n) uses priqueue; local t, x, p, i;
initialize(pq);
insert([-3^n, 3$n], pq);
do
t:= extract(pq);
x:= -t[1];
if numtheory:-bigomega(x-1)=n then return x-1
elif numtheory:-bigomega(x+1)=n then return x
fi;
p:= nextprime(t[-1]);
for i from n+1 to 2 by -1 while t[i] = t[-1] do
insert([t[1]*(p/t[-1])^(n+2-i), op(t[2..i-1]), p$(n+2-i)], pq)
od;
od
end proc:
seq(f(i), i=1..27); # Robert Israel, Sep 30 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 16 2006
EXTENSIONS
a(13)-a(15) from Martin Fuller, Jan 17 2006
a(16)-a(17) from Donovan Johnson, Apr 08 2008
a(18)-a(22) from Donovan Johnson, Jan 21 2009
a(23)-a(25) from Donovan Johnson, May 25 2013
a(26)-a(27) from Robert Israel, Sep 30 2024
STATUS
approved