Adding to 51 its reverse (15), we get a palindrome (66).
Subtracting from 51 its reverse (15), we obtain a triangular number (36 = T8).
51 is nontrivially palindromic in base 2, base 4 and base 16.
51 is an esthetic number in base 6, base 9 and base 12, because in such bases its adjacent digits differ by 1.
It is a 5-Lehmer number, since φ(51) divides (51-1)5.
It is the 6-th Motzkin number.
It is a cyclic number.
It is a D-number.
51 is an undulating number in base 4.
It is the 14-th Perrin number.
51 is a lucky number.
51 is a nontrivial repdigit in base 16.
It is a plaindrome in base 6, base 9, base 11, base 13, base 14, base 15 and base 16.
It is a nialpdrome in base 8, base 10, base 12 and base 16.
It is a zygodrome in base 2 and base 16.
A polygon with 51 sides can be constructed with ruler and compass.
51 is the 6-th pentagonal number.
51 is the 5-th centered pentagonal number.
51 is a wasteful number, since it uses less digits than its factorization.
51 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 20.
The square root of 51 is about 7.1414284285. The cubic root of 51 is about 3.7084297693.