21291481 has 4 divisors (see below), whose sum is σ = 22025700. Its totient is φ = 20557264.

The previous prime is 21291467. The next prime is 21291499. The reversal of 21291481 is 18419212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15531481 + 5760000 = 3941^2 + 2400^2 .

It is a cyclic number.

It is not a de Polignac number, because 21291481 - 2⁵ = 21291449 is a prime.

It is a super-2 number, since 2×21291481² = 906654326346722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21211481) 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, 367066 + ... + 367123.

It is an arithmetic number, because the mean of its divisors is an integer number (5506425).

Almost surely, 2^21291481 is an apocalyptic number.

It is an amenable number.

21291481 is a deficient number, since it is larger than the sum of its proper divisors (734219).

21291481 is an equidigital number, since it uses as much as digits as its factorization.

21291481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 734218.

The product of its digits is 1152, while the sum is 28.

The square root of 21291481 is about 4614.2692812622. The cubic root of 21291481 is about 277.1630235871.

The spelling of 21291481 in words is "twenty-one million, two hundred ninety-one thousand, four hundred eighty-one".