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A355555
a(n) is the first prime prime(j) such that prime(j) + prime(k) + prime(k+1) is prime for k = j+1..j+n but not k = j+n+1.
0
2, 17, 5, 7, 53, 197, 848699, 2802313, 24281267, 54927644129, 29566753319
OFFSET
0,1
COMMENTS
a(11) > 2*10^12. - Iain Fox, Jul 09 2022
EXAMPLE
a(3) = 7 because 7+11+13 = 31, 7+13+17 = 37 and 7+17+19 = 41 are prime but 7+19+23 = 49 is not.
MAPLE
V:= Array(0..8): count:= 0:
f:= proc(n) local p, i;
p:= ithprime(n);
for i from 0 do
if not isprime(p+ithprime(n+i+1)+ithprime(n+i+2)) then return i fi
od
end proc:
for nn from 1 while count < 9 do
v:= f(nn);
if V[v] = 0 then V[v]:= ithprime(nn) fi;
od:
convert(V, list);
PROG
(PARI) a(n) = my(pk, pk1); forprime(pj=2, oo, pk=nextprime(pj+1); for(x=0, n, pk1=nextprime(pk+1); if(!bitxor(x==n, isprime(pj+pk+pk1)), next(2)); pk=pk1); return(pj)) \\ Iain Fox, Jul 06 2022
CROSSREFS
Cf. A000040.
Sequence in context: A144212 A186683 A210492 * A370111 A057280 A055677
KEYWORD
nonn,more,hard
AUTHOR
J. M. Bergot and Robert Israel, Jul 06 2022
EXTENSIONS
a(9)-a(10) from Iain Fox, Jul 06 2022
STATUS
approved