21138381 has 32 divisors (see below), whose sum is σ = 34544640. Its totient is φ = 12668400.

The previous prime is 21138379. The next prime is 21138401. The reversal of 21138381 is 18383112.

It is not a de Polignac number, because 21138381 - 2¹ = 21138379 is a prime.

It is a super-2 number, since 2×21138381² = 893662302602322, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138371) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 30246 + ... + 30936.

It is an arithmetic number, because the mean of its divisors is an integer number (1079520).

Almost surely, 2^21138381 is an apocalyptic number.

It is an amenable number.

21138381 is a deficient number, since it is larger than the sum of its proper divisors (13406259).

21138381 is a wasteful number, since it uses less digits than its factorization.

21138381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 814 (or 808 counting only the distinct ones).

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

The square root of 21138381 is about 4597.6495081726. The cubic root of 21138381 is about 276.4970956512.

The spelling of 21138381 in words is "twenty-one million, one hundred thirty-eight thousand, three hundred eighty-one".