26

This number is a composite.

The number obtained by concatenating the first prime and twice the next prime. [Russo]

The prime factorization of 26 uses the first three counting numbers. [Trotter]

One of only two numbers which contain exactly the first three digits in its unique prime factorization. [Hunter]

The number of minimal primes which cover the set of primes in base 10. [Rupinski]

26 is the smallest number that can be expressed by three identical prime digits in a prime base, i.e., 222 in base three. Note that it is also the reverse of the second such number: 62 = 222 in base 5. [Necula]

26 = 2 * prime(6). [Gupta]

There are no twin primes between 26² and 28². [Wesolowski]

The only number n < 1000 such that 10^n plus or minus 123456789 are both primes. [Loungrides]

The largest of three successive numbers n, n-1, n-2 such that the product of each of them with its reversal plus 1 is prime, i.e., 26*62+1=1613, 25*52+1=1301, 24*42+1=1009. [Loungrides]

The number of primes that end in 3 among the first 100 primes. A greater number than endings 1, 7, or 9. [Honaker]