OFFSET
1,2
COMMENTS
Numbers k such that there is no m < sqrt(k) for which k mod (m^2) is prime.
No more terms up to 2*10^7. I conjecture that these are all the terms.
EXAMPLE
a(7) = 17 is in the sequence because 17 mod (2^2) = 1, 17 mod (3^2) = 8 and 17 mod (4^2) = 1 are all nonprime while 5^2 > 17.
20 is not in the sequence because 20 mod (3^2) = 2 is prime and 3^2 < 20.
MAPLE
filter:= proc(n) local k;
for k from 2 to floor(sqrt(n)) do if isprime(n mod k^2) then return false fi od:
true
end proc:
select(filter, [$1..10^6]);
PROG
(Magma) [m:m in [1..2000]| #[k:k in [2..Floor(Sqrt(m))]| IsPrime(m mod k^2) ] eq 0]; // Marius A. Burtea, Nov 11 2019
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Israel, Nov 10 2019
STATUS
approved