21900421 has 2 divisors, whose sum is σ = 21900422. Its totient is φ = 21900420.

The previous prime is 21900419. The next prime is 21900427. The reversal of 21900421 is 12400912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21390625 + 509796 = 4625^2 + 714^2 .

It is a cyclic number.

It is not a de Polignac number, because 21900421 - 2¹ = 21900419 is a prime.

Together with 21900419, 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 (21900427) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10950210 + 10950211.

It is an arithmetic number, because the mean of its divisors is an integer number (10950211).

Almost surely, 2^21900421 is an apocalyptic number.

It is an amenable number.

21900421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21900421 is an equidigital number, since it uses as much as digits as its factorization.

21900421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21900421 is about 4679.7885635999. The cubic root of 21900421 is about 279.7805295496.

The spelling of 21900421 in words is "twenty-one million, nine hundred thousand, four hundred twenty-one".