21621381 has 8 divisors (see below), whose sum is σ = 28965984. Its totient is φ = 14345520.

The previous prime is 21621377. The next prime is 21621401. The reversal of 21621381 is 18312612.

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

It is not a de Polignac number, because 21621381 - 2² = 21621377 is a prime.

It is a super-2 number, since 2×21621381² = 934968232694322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621371) 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, 16446 + ... + 17711.

It is an arithmetic number, because the mean of its divisors is an integer number (3620748).

Almost surely, 2^21621381 is an apocalyptic number.

It is an amenable number.

21621381 is a deficient number, since it is larger than the sum of its proper divisors (7344603).

21621381 is a wasteful number, since it uses less digits than its factorization.

21621381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34371.

The product of its digits is 576, while the sum is 24.

The square root of 21621381 is about 4649.8796758626. The cubic root of 21621381 is about 278.5871902794.

Adding to 21621381 its reverse (18312612), we get a palindrome (39933993).

The spelling of 21621381 in words is "twenty-one million, six hundred twenty-one thousand, three hundred eighty-one".