21481921 has 2 divisors, whose sum is σ = 21481922. Its totient is φ = 21481920.

The previous prime is 21481919. The next prime is 21481927. The reversal of 21481921 is 12918412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20976400 + 505521 = 4580^2 + 711^2 .

It is a cyclic number.

It is not a de Polignac number, because 21481921 - 2¹ = 21481919 is a prime.

It is a super-2 number, since 2×21481921² = 922945859700482, which contains 22 as substring.

Together with 21481919, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21481921.

It is not a weakly prime, because it can be changed into another prime (21481927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10740960 + 10740961.

It is an arithmetic number, because the mean of its divisors is an integer number (10740961).

Almost surely, 2^21481921 is an apocalyptic number.

It is an amenable number.

21481921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21481921 is an equidigital number, since it uses as much as digits as its factorization.

21481921 is an evil number, because the sum of its binary digits is even.

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

The square root of 21481921 is about 4634.8593290412. The cubic root of 21481921 is about 277.9869263904.

It can be divided in two parts, 214819 and 21, that added together give a triangular number (214840 = T₆₅₅).

The spelling of 21481921 in words is "twenty-one million, four hundred eighty-one thousand, nine hundred twenty-one".