# 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 26^{2} and
28^{2}. [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]