15661921 has 8 divisors (see below), whose sum is σ = 17114688. Its totient is φ = 14214000.

The previous prime is 15661907. The next prime is 15661937. The reversal of 15661921 is 12916651.

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 15661921 - 2⁵ = 15661889 is a prime.

It is a super-3 number, since 3×15661921³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15661991) 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, 10651 + ... + 12031.

It is an arithmetic number, because the mean of its divisors is an integer number (2139336).

Almost surely, 2^15661921 is an apocalyptic number.

15661921 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

15661921 is a deficient number, since it is larger than the sum of its proper divisors (1452767).

15661921 is a wasteful number, since it uses less digits than its factorization.

15661921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2423.

The product of its digits is 3240, while the sum is 31.

The square root of 15661921 is about 3957.5144977625. The cubic root of 15661921 is about 250.1967571059.

The spelling of 15661921 in words is "fifteen million, six hundred sixty-one thousand, nine hundred twenty-one".