21490381 has 8 divisors (see below), whose sum is σ = 23521824. Its totient is φ = 19471920.

The previous prime is 21490319. The next prime is 21490393. The reversal of 21490381 is 18309412.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21490381 - 2¹⁹ = 20966093 is a prime.

It is a super-2 number, since 2×21490381² = 923672951050322, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21490181) 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, 406 + ... + 6568.

It is an arithmetic number, because the mean of its divisors is an integer number (2940228).

Almost surely, 2^21490381 is an apocalyptic number.

It is an amenable number.

21490381 is a deficient number, since it is larger than the sum of its proper divisors (2031443).

21490381 is a wasteful number, since it uses less digits than its factorization.

21490381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6491.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21490381 is about 4635.7718882620. The cubic root of 21490381 is about 278.0234138277.

Adding to 21490381 its reverse (18309412), we get a palindrome (39799793).

The spelling of 21490381 in words is "twenty-one million, four hundred ninety thousand, three hundred eighty-one".