651691921 has 4 divisors (see below), whose sum is σ = 651743344. Its totient is φ = 651640500.

The previous prime is 651691919. The next prime is 651691927. The reversal of 651691921 is 129196156.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 651691921 - 2¹ = 651691919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (651691927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8266 + ... + 37036.

It is an arithmetic number, because the mean of its divisors is an integer number (162935836).

Almost surely, 2^651691921 is an apocalyptic number.

It is an amenable number.

651691921 is a deficient number, since it is larger than the sum of its proper divisors (51423).

651691921 is a wasteful number, since it uses less digits than its factorization.

651691921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51422.

The product of its digits is 29160, while the sum is 40.

The square root of 651691921 is about 25528.2573044068. The cubic root of 651691921 is about 866.9900480750.

The spelling of 651691921 in words is "six hundred fifty-one million, six hundred ninety-one thousand, nine hundred twenty-one".