%I #13 Feb 25 2021 21:27:03
%S 83,97,107,127,157,167,193,233,239,257,263,269,281,293,307,311,313,
%T 317,347,349,359,367,383,401,409,419,431,439,457,467,487,499,503,521,
%U 523,563,569,577,593,599,601,607,617,653,661,677,683,691,719,743,757,769,773,797,811,821,839,853
%N Isolated primes in the hexagonal spiral of the nonnegative integers.
%C Plotting the integers on a hexagonal grid as in A001399 associates each n>=0 with six different neighbors to the E, NE, NW, W, SE and SW. If n is prime and all 6 neighbors are composite, n is in the sequence.
%e The six neighbors of the prime 7 are 1, 6, 8, 18, 19, 20; 19 is also prime, so 7 is not in the sequence.
%e The six neighbors of the prime 83 are 54, 55, 82, 84, 117 and 118 which are all composite, so 83 is in the sequence.
%p # replace isA001358 by isprime in the coding for A113653, and isA113653 by isA335916.
%Y Cf. A001399, A113653 (isolated semiprimes).
%K nonn
%O 1,1
%A _R. J. Mathar_, Jun 29 2020