21435391 has 2 divisors, whose sum is σ = 21435392. Its totient is φ = 21435390.

The previous prime is 21435389. The next prime is 21435409. The reversal of 21435391 is 19353412.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21435391 - 2¹ = 21435389 is a prime.

Together with 21435389, 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 (21435311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10717695 + 10717696.

It is an arithmetic number, because the mean of its divisors is an integer number (10717696).

Almost surely, 2^21435391 is an apocalyptic number.

21435391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21435391 is an equidigital number, since it uses as much as digits as its factorization.

21435391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 28.

The square root of 21435391 is about 4629.8370381688. The cubic root of 21435391 is about 277.7860740574.

It can be divided in two parts, 2 and 1435391, that multiplied together give a palindrome (2870782).

The spelling of 21435391 in words is "twenty-one million, four hundred thirty-five thousand, three hundred ninety-one".