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 that is directly between a prime square and a prime cube. [Gudipati]
The first nth semiprime which is smaller than the nth prime. [Silva]
Smallest non-palindromic non-prime n such that the product of its divisors is a palindrome. [Post]
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]
26 is the third term in the following sequence:
a(n) is the height (continuous number of rows) of a palindromic prime pyramid
(starting with 2) of step size n, where each palindromic
prime p is the smallest p that contains p in the row above. The sequence begins: 3, 11, 26, 135, 828, ... . [Honaker]