OFFSET
1,1
COMMENTS
If n = p_1 * ... * p_m with primes p_i <= p_{i+1}, then p_1 + p_1*p_2 + ... + p_1*p_2*...*p_m + p2*...*p_m + ... + p_m is prime.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(5)=20 is a term because 20=2*2*5 and 2+2*2+2*2*5+2*5+5 = 41 is prime.
MAPLE
filter:= proc(n) local L, m;
L:= sort(map(t -> t[1]$t[2], ifactors(n)[2]));
m:= nops(L);
if m=1 then return false fi;
isprime(n + add(mul(L[i], i=1..j)+mul(L[i], i=j+1..m), j=1..m-1))
end proc:
select(filter, [$4..300]);
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Dec 04 2020
STATUS
approved