21238981 has 2 divisors, whose sum is σ = 21238982. Its totient is φ = 21238980.

The previous prime is 21238969. The next prime is 21239027. The reversal of 21238981 is 18983212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20848356 + 390625 = 4566^2 + 625^2 .

It is a cyclic number.

It is not a de Polignac number, because 21238981 - 2⁵ = 21238949 is a prime.

It is a super-2 number, since 2×21238981² = 902188627836722, which contains 22 as substring.

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

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21238901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10619490 + 10619491.

It is an arithmetic number, because the mean of its divisors is an integer number (10619491).

Almost surely, 2^21238981 is an apocalyptic number.

It is an amenable number.

21238981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21238981 is an equidigital number, since it uses as much as digits as its factorization.

21238981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6912, while the sum is 34.

The square root of 21238981 is about 4608.5768953116. The cubic root of 21238981 is about 276.9350288783.

It can be divided in two parts, 212 and 38981, that added together give a palindrome (39193).

The spelling of 21238981 in words is "twenty-one million, two hundred thirty-eight thousand, nine hundred eighty-one".