21508373 has 2 divisors, whose sum is σ = 21508374. Its totient is φ = 21508372.

The previous prime is 21508337. The next prime is 21508379. The reversal of 21508373 is 37380512.

Together with previous prime (21508337) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19864849 + 1643524 = 4457^2 + 1282^2 .

It is a cyclic number.

It is not a de Polignac number, because 21508373 - 2⁶ = 21508309 is a prime.

It is a super-2 number, since 2×21508373² = 925220218214258, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21508379) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10754186 + 10754187.

It is an arithmetic number, because the mean of its divisors is an integer number (10754187).

Almost surely, 2^21508373 is an apocalyptic number.

It is an amenable number.

21508373 is a deficient number, since it is larger than the sum of its proper divisors (1).

21508373 is an equidigital number, since it uses as much as digits as its factorization.

21508373 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5040, while the sum is 29.

The square root of 21508373 is about 4637.7120436698. The cubic root of 21508373 is about 278.1009803437.

Adding to 21508373 its reverse (37380512), we get a palindrome (58888885).

The spelling of 21508373 in words is "twenty-one million, five hundred eight thousand, three hundred seventy-three".