21387481 has 8 divisors (see below), whose sum is σ = 21759840. Its totient is φ = 21018528.

The previous prime is 21387473. The next prime is 21387497. The reversal of 21387481 is 18478312.

It is a happy number.

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 21387481 - 2³ = 21387473 is a prime.

It is a super-2 number, since 2×21387481² = 914848687050722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21387451) 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, 13930 + ... + 15388.

It is an arithmetic number, because the mean of its divisors is an integer number (2719980).

Almost surely, 2^21387481 is an apocalyptic number.

It is an amenable number.

21387481 is a deficient number, since it is larger than the sum of its proper divisors (372359).

21387481 is a wasteful number, since it uses less digits than its factorization.

21387481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1703.

The product of its digits is 10752, while the sum is 34.

The square root of 21387481 is about 4624.6600956178. The cubic root of 21387481 is about 277.5789608377.

The spelling of 21387481 in words is "twenty-one million, three hundred eighty-seven thousand, four hundred eighty-one".