1681
This number is a composite.
First square K with prime triplets K-18, K-14, K-12, K+12,
K+16, K+18 as nearest primes (next one, if any, is over
10^7). [Wood]
The smallest composite (semiprime) generated from Euler's famous prime polynomial x^2+x+41. [Gupta]
The smallest square whose representations in septenary,
octal and nonary (4621, 3221, 2267) are all prime when read
in decimal. Note that 1681 = 2^4||3^4 i.e., concatenation
of fourth-powers of first two primes. [Bajpai]
Printed from the PrimePages <t5k.org> © G. L. Honaker and Chris K. Caldwell