651 has 8 divisors (see below), whose sum is σ = 1024. Its totient is φ = 360.

The previous prime is 647. The next prime is 653. The reversal of 651 is 156.

651 = T₁₀ + T₁₁ + ... + T₁₆.

651 is nontrivially palindromic in base 5 and base 6.

651 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

651 is an esthetic number in base 5, because in such base its adjacent digits differ by 1.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 651 - 2² = 647 is a prime.

It is the 26-th Hogben number.

It is a Duffinian number.

651 is an undulating number in base 5.

651 is a lucky number.

It is a plaindrome in base 14 and base 16.

It is a nialpdrome in base 10 and base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (653) by changing a digit.

It is a nontrivial repunit in base 25.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6 + ... + 36.

It is an arithmetic number, because the mean of its divisors is an integer number (128).

651 is the 21-st pentagonal number and also the 14-th nonagonal number.

651 is a deficient number, since it is larger than the sum of its proper divisors (373).

651 is a wasteful number, since it uses less digits than its factorization.

651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41.

The product of its digits is 30, while the sum is 12.

The square root of 651 is about 25.5147016443. The cubic root of 651 is about 8.6668310291. Note that the first 3 decimals are identical.

It can be divided in two parts, 65 and 1, that added together give a palindrome (66).

The spelling of 651 in words is "six hundred fifty-one", and thus it is an aban number.