65521621721 has 8 divisors (see below), whose sum is σ = 65791187904. Its totient is φ = 65252451600.

The previous prime is 65521621673. The next prime is 65521621729. The reversal of 65521621721 is 12712612556.

65521621721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is a cyclic number.

It is not a de Polignac number, because 65521621721 - 2¹⁸ = 65521359577 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (65521621729) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 234836 + ... + 431498.

It is an arithmetic number, because the mean of its divisors is an integer number (8223898488).

Almost surely, 2^65521621721 is an apocalyptic number.

It is an amenable number.

65521621721 is a deficient number, since it is larger than the sum of its proper divisors (269566183).

65521621721 is a wasteful number, since it uses less digits than its factorization.

65521621721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 198031.

The product of its digits is 50400, while the sum is 38.

The spelling of 65521621721 in words is "sixty-five billion, five hundred twenty-one million, six hundred twenty-one thousand, seven hundred twenty-one".