21400981 has 4 divisors (see below), whose sum is σ = 24458272. Its totient is φ = 18343692.

The previous prime is 21400979. The next prime is 21400997. The reversal of 21400981 is 18900412.

It is a happy number.

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 not a de Polignac number, because 21400981 - 2¹ = 21400979 is a prime.

It is a super-2 number, since 2×21400981² = 916003975524722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21400921) 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, 1528635 + ... + 1528648.

It is an arithmetic number, because the mean of its divisors is an integer number (6114568).

Almost surely, 2^21400981 is an apocalyptic number.

It is an amenable number.

21400981 is a deficient number, since it is larger than the sum of its proper divisors (3057291).

21400981 is an equidigital number, since it uses as much as digits as its factorization.

21400981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3057290.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21400981 is about 4626.1194320942. The cubic root of 21400981 is about 277.6373521274.

The spelling of 21400981 in words is "twenty-one million, four hundred thousand, nine hundred eighty-one".