15421721 has 12 divisors (see below), whose sum is σ = 18011088. Its totient is φ = 13165992.

The previous prime is 15421709. The next prime is 15421723. The reversal of 15421721 is 12712451.

15421721 is digitally balanced in base 2 and base 8, because in such bases it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 15421721 - 2¹⁸ = 15159577 is a prime.

It is a Duffinian number.

15421721 is strictly pandigital in base 8.

It is not an unprimeable number, because it can be changed into a prime (15421723) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 16550 + ... + 17456.

It is an arithmetic number, because the mean of its divisors is an integer number (1500924).

Almost surely, 2^15421721 is an apocalyptic number.

It is an amenable number.

15421721 is a deficient number, since it is larger than the sum of its proper divisors (2589367).

15421721 is an equidigital number, since it uses as much as digits as its factorization.

15421721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1268 (or 1261 counting only the distinct ones).

The product of its digits is 560, while the sum is 23.

The square root of 15421721 is about 3927.0499105563. The cubic root of 15421721 is about 248.9111094889.

The spelling of 15421721 in words is "fifteen million, four hundred twenty-one thousand, seven hundred twenty-one".