21921901 has 2 divisors, whose sum is σ = 21921902. Its totient is φ = 21921900.

The previous prime is 21921899. The next prime is 21921917. The reversal of 21921901 is 10912912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21846276 + 75625 = 4674^2 + 275^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921901 - 2¹ = 21921899 is a prime.

Together with 21921899, 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 (21921301) 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, 10960950 + 10960951.

It is an arithmetic number, because the mean of its divisors is an integer number (10960951).

Almost surely, 2^21921901 is an apocalyptic number.

It is an amenable number.

21921901 is a deficient number, since it is larger than the sum of its proper divisors (1).

21921901 is an equidigital number, since it uses as much as digits as its factorization.

21921901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 324, while the sum is 25.

The square root of 21921901 is about 4682.0829766248. The cubic root of 21921901 is about 279.8719695280.

It can be divided in two parts, 21921 and 901, that added together give a palindrome (22822).

The spelling of 21921901 in words is "twenty-one million, nine hundred twenty-one thousand, nine hundred one".