OFFSET
1,3
COMMENTS
No terms == 2 (mod 4). - Robert Israel, Mar 24 2023
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(3)=3 because prime[3]=5 and 5+(3+4+5)=17= is a prime A085418(3).
MAPLE
f:= proc(n) local m, k, x;
m:= ithprime(n) - (n-1)*n/2;
for k from n do
x:= k*(k+1)/2 + m;
if isprime(x) then return k+1-n fi
od;
end proc:
map(f, [$1..100]); # Robert Israel, Mar 24 2023
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Zak Seidov, Jun 30 2003
STATUS
approved