1645721957 has 16 divisors (see below), whose sum is σ = 1858896000. Its totient is φ = 1443234240.

The previous prime is 1645721947. The next prime is 1645721963. The reversal of 1645721957 is 7591275461.

It is a cyclic number.

It is not a de Polignac number, because 1645721957 - 2²² = 1641527653 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1645721947) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 620408 + ... + 623054.

It is an arithmetic number, because the mean of its divisors is an integer number (116181000).

Almost surely, 2^1645721957 is an apocalyptic number.

It is an amenable number.

1645721957 is a deficient number, since it is larger than the sum of its proper divisors (213174043).

1645721957 is a wasteful number, since it uses less digits than its factorization.

1645721957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4636.

The product of its digits is 529200, while the sum is 47.

The square root of 1645721957 is about 40567.4987767301. The cubic root of 1645721957 is about 1180.6436106346.

The spelling of 1645721957 in words is "one billion, six hundred forty-five million, seven hundred twenty-one thousand, nine hundred fifty-seven".