21735421 has 2 divisors, whose sum is σ = 21735422. Its totient is φ = 21735420.

The previous prime is 21735419. The next prime is 21735431. The reversal of 21735421 is 12453712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16695396 + 5040025 = 4086^2 + 2245^2 .

It is a cyclic number.

It is not a de Polignac number, because 21735421 - 2¹ = 21735419 is a prime.

Together with 21735419, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21735431) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10867710 + 10867711.

It is an arithmetic number, because the mean of its divisors is an integer number (10867711).

Almost surely, 2^21735421 is an apocalyptic number.

It is an amenable number.

21735421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21735421 is an equidigital number, since it uses as much as digits as its factorization.

21735421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1680, while the sum is 25.

The square root of 21735421 is about 4662.1262316673. The cubic root of 21735421 is about 279.0761259020.

The spelling of 21735421 in words is "twenty-one million, seven hundred thirty-five thousand, four hundred twenty-one".