OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..2500
EXAMPLE
a(3) = 1911 is a term because 1911 = 5^2+5*41+41^2 = 19^2+19*31+31^2 where 5, 41, 19 and 31 are primes.
MAPLE
N:= 10^6: # for terms <= N
P:= select(isprime, [2, seq(i, i=3..floor(sqrt(N)), 2)]):
nP:= nops(P):
S:= {}: T:= {}:
for i from 1 to nP do
for j from 1 to i do
x:= P[i]^2 + P[i]*P[j]+P[j]^2;
if x > N then break fi;
if member(x, S) then T:= T union {x} fi;
S:= S union {x};
od od:
sort(convert(T, list));
MATHEMATICA
Do[If[Total@Boole[And@@@PrimeQ[{p, q}/.Solve[p^2+p*q+q^2==k&&p>1&&p<=q, {p, q}, Integers]]]>1, Print@k], {k, 10^6}] (* Giorgos Kalogeropoulos, Jan 09 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jan 09 2022
STATUS
approved