15621721645 has 16 divisors (see below), whose sum is σ = 19107487872. Its totient is φ = 12256620480.

The previous prime is 15621721627. The next prime is 15621721681. The reversal of 15621721645 is 54612712651.

It is not a de Polignac number, because 15621721645 - 2¹³ = 15621713453 is a prime.

It is a super-3 number, since 3×15621721645³ (a number of 32 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 15621721598 and 15621721607.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 732280 + ... + 753310.

It is an arithmetic number, because the mean of its divisors is an integer number (1194217992).

Almost surely, 2^15621721645 is an apocalyptic number.

It is an amenable number.

15621721645 is a deficient number, since it is larger than the sum of its proper divisors (3485766227).

15621721645 is a wasteful number, since it uses less digits than its factorization.

15621721645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23892.

The product of its digits is 100800, while the sum is 40.

The spelling of 15621721645 in words is "fifteen billion, six hundred twenty-one million, seven hundred twenty-one thousand, six hundred forty-five".