OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=4, the product of 2*4-1 = 7 primes starting with a(4) = 5 is 5*7*11*13*17*19*23 which is divisible by 5+7+11+13+17+19+23 = 95 = 5*19.
MAPLE
plow:= n -> n*(ln(n)+ln(ln(n))-1):
phi:= n -> n*(ln(n)+ln(ln(n))):
f:= proc(n) local i, k, m, q;
m:= 2*n-1;
for k from 0 do
if mul(ithprime(k+i), i=1..2*n-1) mod add(ithprime(k+i), i=1..2*n-1) = 0 then return ithprime(k+1) fi;
if k >= 5 and is(m*phi(k+m-1) < plow(k)^2) then return 0 fi;
od;
end proc:
map(f, [$1..100]);
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jan 19 2021
STATUS
approved