A176681 Numbers k such that k^2 +-5 are primes.
6, 12, 36, 72, 78, 168, 198, 204, 342, 432, 456, 492, 534, 588, 594, 666, 726, 756, 786, 804, 996, 1014, 1212, 1218, 1248, 1254, 1266, 1314, 1344, 1476, 1512, 1554, 1806, 1812, 1902, 2088, 2298, 2322, 2364, 2616, 2634, 3066, 3072, 3162, 3432, 3444, 3852
Offset: 1
Keywords
Examples
12 is in the sequence, because 12^2 + 5 = 149 and 12^2 - 5 = 139 are primes.
Links
- Daniel Starodubtsev, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Range[8! ],PrimeQ[ #^2-5]&&PrimeQ[ #^2+5]&]