1643637481 has 4 divisors (see below), whose sum is σ = 1656184464. Its totient is φ = 1631090500.

The previous prime is 1643637473. The next prime is 1643637491. The reversal of 1643637481 is 1847363461.

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 1643637481 - 2³ = 1643637473 is a prime.

It is a super-2 number, since 2×1643637481² = 5403088337896050722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1643637491) 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, 6273295 + ... + 6273556.

It is an arithmetic number, because the mean of its divisors is an integer number (414046116).

Almost surely, 2^1643637481 is an apocalyptic number.

It is an amenable number.

1643637481 is a deficient number, since it is larger than the sum of its proper divisors (12546983).

1643637481 is a wasteful number, since it uses less digits than its factorization.

1643637481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12546982.

The product of its digits is 290304, while the sum is 43.

The square root of 1643637481 is about 40541.7991830654. The cubic root of 1643637481 is about 1180.1449312073.

The spelling of 1643637481 in words is "one billion, six hundred forty-three million, six hundred thirty-seven thousand, four hundred eighty-one".