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A340575
a(n) is the least prime p such that the product of 2*n-1 consecutive primes starting with p is divisible by the sum of those same primes, or 0 if there is no such prime.
1
2, 2, 3, 5, 5, 3, 2, 11, 7, 7, 5, 2, 3, 0, 3, 7, 11, 7, 31, 2, 2, 2, 5, 13, 3, 3, 2, 71, 2, 3, 31, 109, 71, 7, 3, 0, 2, 59, 2, 17, 3, 5, 61, 0, 29, 17, 41, 29, 5, 3, 5, 3, 11, 79, 0, 41, 3, 11, 5, 5, 5, 37, 37, 59, 13, 3, 3, 3, 31, 31, 61, 2, 2, 3, 2, 2, 2, 23, 2, 5, 11, 5, 7, 2, 5, 5, 67, 5, 0
OFFSET
1,1
LINKS
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
Sequence in context: A284114 A323480 A330404 * A139171 A329570 A279724
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jan 19 2021
STATUS
approved