15217921 has 4 divisors (see below), whose sum is σ = 15243844. Its totient is φ = 15192000.

The previous prime is 15217919. The next prime is 15217963. The reversal of 15217921 is 12971251.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12971251 = 43 ⋅301657.

It can be written as a sum of positive squares in 2 ways, for example, as 12531600 + 2686321 = 3540^2 + 1639^2 .

It is a cyclic number.

It is not a de Polignac number, because 15217921 - 2¹ = 15217919 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 15217921.

It is not an unprimeable number, because it can be changed into a prime (15217901) 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, 12060 + ... + 13261.

It is an arithmetic number, because the mean of its divisors is an integer number (3810961).

Almost surely, 2^15217921 is an apocalyptic number.

It is an amenable number.

15217921 is a deficient number, since it is larger than the sum of its proper divisors (25923).

15217921 is an equidigital number, since it uses as much as digits as its factorization.

15217921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25922.

The product of its digits is 1260, while the sum is 28.

The square root of 15217921 is about 3901.0153806413. The cubic root of 15217921 is about 247.8097797768.

It can be divided in two parts, 1521 and 7921, that multiplied together give a square (12047841 = 3471²).

The spelling of 15217921 in words is "fifteen million, two hundred seventeen thousand, nine hundred twenty-one".