21520423 has 2 divisors, whose sum is σ = 21520424. Its totient is φ = 21520422.

The previous prime is 21520399. The next prime is 21520441. The reversal of 21520423 is 32402512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21520423 - 2⁵ = 21520391 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21520423.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21520463) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760211 + 10760212.

It is an arithmetic number, because the mean of its divisors is an integer number (10760212).

Almost surely, 2^21520423 is an apocalyptic number.

21520423 is a deficient number, since it is larger than the sum of its proper divisors (1).

21520423 is an equidigital number, since it uses as much as digits as its factorization.

21520423 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21520423 is about 4639.0109937356. The cubic root of 21520423 is about 278.1529057216.

Adding to 21520423 its reverse (32402512), we get a palindrome (53922935).

The spelling of 21520423 in words is "twenty-one million, five hundred twenty thousand, four hundred twenty-three".