509721921 has 6 divisors (see below), whose sum is σ = 736265010. Its totient is φ = 339814608.

The previous prime is 509721899. The next prime is 509721943. The reversal of 509721921 is 129127905.

It is an interprime number because it is at equal distance from previous prime (509721899) and next prime (509721943).

It can be written as a sum of positive squares in only one way, i.e., 477641025 + 32080896 = 21855^2 + 5664^2 .

It is not a de Polignac number, because 509721921 - 2⁶ = 509721857 is a prime.

It is not an unprimeable number, because it can be changed into a prime (509721221) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 28317876 + ... + 28317893.

It is an arithmetic number, because the mean of its divisors is an integer number (122710835).

Almost surely, 2^509721921 is an apocalyptic number.

It is an amenable number.

509721921 is a deficient number, since it is larger than the sum of its proper divisors (226543089).

509721921 is a wasteful number, since it uses less digits than its factorization.

509721921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56635775 (or 56635772 counting only the distinct ones).

The product of its (nonzero) digits is 11340, while the sum is 36.

The square root of 509721921 is about 22577.0219692501. The cubic root of 509721921 is about 798.8117364318.

The spelling of 509721921 in words is "five hundred nine million, seven hundred twenty-one thousand, nine hundred twenty-one".