cp's OEIS Frontend

A342609 Positive integers that cannot be written in the form k - gpf(k) +- 1 for some integer k, where gpf(k) is the greatest prime factor of k.

%I A342609 #15 Apr 12 2021 21:45:37
%S A342609 17,49,161,197,199,209,251,391,419,449,649,685,769,799,883,967,1057,
%T A342609 1189,1249,1301,1457,1481,1681,1793,1937,1979,2001,2029,2089,2177,
%U A342609 2209,2311,2377,2379,2419,2431,2449,2549,2551,2575,2591,2705,2729,2899,3041,3073
%N A342609 Positive integers that cannot be written in the form k - gpf(k) +- 1 for some integer k, where gpf(k) is the greatest prime factor of k.
%H A342609 Robert Israel, <a href="/A342609/b342609.txt">Table of n, a(n) for n = 1..10000</a>
%p A342609 f:= proc(n) local g;
%p A342609   g:= max(numtheory:-factorset(n));
%p A342609   n-g+1,n-g-1
%p A342609 end proc:
%p A342609 sort(convert({$1..5000} minus map(f, {$1..10001}),list)); # _Robert Israel_, Apr 12 2021
%Y A342609 Cf. A006530, A076563.
%K A342609 nonn
%O A342609 1,1
%A A342609 _Christian Bagshaw_, Mar 16 2021