65721521 has 4 divisors (see below), whose sum is σ = 66223344. Its totient is φ = 65219700.

The previous prime is 65721499. The next prime is 65721533. The reversal of 65721521 is 12512756.

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 a de Polignac number, because none of the positive numbers 2^k-65721521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (65721121) 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, 250715 + ... + 250976.

It is an arithmetic number, because the mean of its divisors is an integer number (16555836).

Almost surely, 2^65721521 is an apocalyptic number.

It is an amenable number.

65721521 is a deficient number, since it is larger than the sum of its proper divisors (501823).

65721521 is a wasteful number, since it uses less digits than its factorization.

65721521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 501822.

The product of its digits is 4200, while the sum is 29.

The square root of 65721521 is about 8106.8810895436. The cubic root of 65721521 is about 403.5548166931.

The spelling of 65721521 in words is "sixty-five million, seven hundred twenty-one thousand, five hundred twenty-one".