21157481 has 4 divisors (see below), whose sum is σ = 21264000. Its totient is φ = 21050964.

The previous prime is 21157463. The next prime is 21157483. The reversal of 21157481 is 18475112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21157481 is a prime.

It is a super-2 number, since 2×21157481² = 895278004530722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21157483) 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, 52961 + ... + 53358.

It is an arithmetic number, because the mean of its divisors is an integer number (5316000).

Almost surely, 2^21157481 is an apocalyptic number.

It is an amenable number.

21157481 is a deficient number, since it is larger than the sum of its proper divisors (106519).

21157481 is a wasteful number, since it uses less digits than its factorization.

21157481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 106518.

The product of its digits is 2240, while the sum is 29.

The square root of 21157481 is about 4599.7261875029. The cubic root of 21157481 is about 276.5803487113.

The spelling of 21157481 in words is "twenty-one million, one hundred fifty-seven thousand, four hundred eighty-one".