21750247 has 4 divisors (see below), whose sum is σ = 21880656. Its totient is φ = 21619840.

The previous prime is 21750241. The next prime is 21750271. The reversal of 21750247 is 74205712.

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 21750247 - 2⁷ = 21750119 is a prime.

It is a super-2 number, since 2×21750247² = 946146489122018, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21750241) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64954 + ... + 65287.

It is an arithmetic number, because the mean of its divisors is an integer number (5470164).

Almost surely, 2^21750247 is an apocalyptic number.

21750247 is a deficient number, since it is larger than the sum of its proper divisors (130409).

21750247 is a wasteful number, since it uses less digits than its factorization.

21750247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130408.

The product of its (nonzero) digits is 3920, while the sum is 28.

The square root of 21750247 is about 4663.7160076488. The cubic root of 21750247 is about 279.1395652412.

Adding to 21750247 its reverse (74205712), we get a palindrome (95955959).

The spelling of 21750247 in words is "twenty-one million, seven hundred fifty thousand, two hundred forty-seven".