21372251 has 4 divisors (see below), whose sum is σ = 21629832. Its totient is φ = 21114672.

The previous prime is 21372233. The next prime is 21372269. The reversal of 21372251 is 15227312.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21372233) and next prime (21372269).

It is a cyclic number.

It is not a de Polignac number, because 21372251 - 2⁶ = 21372187 is a prime.

It is a super-2 number, since 2×21372251² = 913546225614002, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21372271) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 128666 + ... + 128831.

It is an arithmetic number, because the mean of its divisors is an integer number (5407458).

Almost surely, 2^21372251 is an apocalyptic number.

21372251 is a deficient number, since it is larger than the sum of its proper divisors (257581).

21372251 is an equidigital number, since it uses as much as digits as its factorization.

21372251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 257580.

The product of its digits is 840, while the sum is 23.

The square root of 21372251 is about 4623.0131948763. The cubic root of 21372251 is about 277.5130573084.

Adding to 21372251 its reverse (15227312), we get a palindrome (36599563).

The spelling of 21372251 in words is "twenty-one million, three hundred seventy-two thousand, two hundred fifty-one".