21240981 has 8 divisors (see below), whose sum is σ = 31468160. Its totient is φ = 14160636.

The previous prime is 21240977. The next prime is 21240991. The reversal of 21240981 is 18904212.

It is not a de Polignac number, because 21240981 - 2² = 21240977 is a prime.

It is a super-2 number, since 2×21240981² = 902358547684722, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 786703 = 21240981 / (2 + 1 + 2 + 4 + 0 + 9 + 8 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21240971) 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, 393325 + ... + 393378.

It is an arithmetic number, because the mean of its divisors is an integer number (3933520).

Almost surely, 2^21240981 is an apocalyptic number.

It is an amenable number.

21240981 is a deficient number, since it is larger than the sum of its proper divisors (10227179).

21240981 is an equidigital number, since it uses as much as digits as its factorization.

21240981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 786712 (or 786706 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 27.

The square root of 21240981 is about 4608.7938769270. The cubic root of 21240981 is about 276.9437212708.

The spelling of 21240981 in words is "twenty-one million, two hundred forty thousand, nine hundred eighty-one".