21421981 has 8 divisors (see below), whose sum is σ = 25326720. Its totient is φ = 17728368.

The previous prime is 21421943. The next prime is 21421997. The reversal of 21421981 is 18912412.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21421981 - 2¹¹ = 21419933 is a prime.

It is a super-2 number, since 2×21421981² = 917802539928722, 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 (21421931) 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, 52561 + ... + 52966.

It is an arithmetic number, because the mean of its divisors is an integer number (3165840).

Almost surely, 2^21421981 is an apocalyptic number.

It is an amenable number.

21421981 is a deficient number, since it is larger than the sum of its proper divisors (3904739).

21421981 is a wasteful number, since it uses less digits than its factorization.

21421981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 105563.

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

The square root of 21421981 is about 4628.3885964772. The cubic root of 21421981 is about 277.7281342336.

The spelling of 21421981 in words is "twenty-one million, four hundred twenty-one thousand, nine hundred eighty-one".