651138721 has 4 divisors (see below), whose sum is σ = 685409200. Its totient is φ = 616868244.

The previous prime is 651138713. The next prime is 651138731. The reversal of 651138721 is 127831156.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 651138721 - 2³ = 651138713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (651138701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17135211 + ... + 17135248.

It is an arithmetic number, because the mean of its divisors is an integer number (171352300).

Almost surely, 2^651138721 is an apocalyptic number.

It is an amenable number.

651138721 is a deficient number, since it is larger than the sum of its proper divisors (34270479).

651138721 is a wasteful number, since it uses less digits than its factorization.

651138721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34270478.

The product of its digits is 10080, while the sum is 34.

The square root of 651138721 is about 25517.4199518682. The cubic root of 651138721 is about 866.7446587767.

Adding to 651138721 its reverse (127831156), we get a palindrome (778969877).

The spelling of 651138721 in words is "six hundred fifty-one million, one hundred thirty-eight thousand, seven hundred twenty-one".