21672251 has 4 divisors (see below), whose sum is σ = 22419600. Its totient is φ = 20924904.

The previous prime is 21672239. The next prime is 21672271. The reversal of 21672251 is 15227612.

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

It is a cyclic number.

It is not a de Polignac number, because 21672251 - 2¹⁴ = 21655867 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21672251.

It is not an unprimeable number, because it can be changed into a prime (21672221) 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, 373631 + ... + 373688.

It is an arithmetic number, because the mean of its divisors is an integer number (5604900).

Almost surely, 2^21672251 is an apocalyptic number.

21672251 is a deficient number, since it is larger than the sum of its proper divisors (747349).

21672251 is an equidigital number, since it uses as much as digits as its factorization.

21672251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 747348.

The product of its digits is 1680, while the sum is 26.

The square root of 21672251 is about 4655.3464962342. The cubic root of 21672251 is about 278.8055024312.

Adding to 21672251 its reverse (15227612), we get a palindrome (36899863).

The spelling of 21672251 in words is "twenty-one million, six hundred seventy-two thousand, two hundred fifty-one".