21657869 has 4 divisors (see below), whose sum is σ = 21881244. Its totient is φ = 21434496.

The previous prime is 21657863. The next prime is 21657877. The reversal of 21657869 is 96875612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 12687844 + 8970025 = 3562^2 + 2995^2 .

It is a cyclic number.

It is not a de Polignac number, because 21657869 - 2¹² = 21653773 is a prime.

It is a super-2 number, since 2×21657869² = 938126579242322, 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 (21657863) 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, 111542 + ... + 111735.

It is an arithmetic number, because the mean of its divisors is an integer number (5470311).

Almost surely, 2^21657869 is an apocalyptic number.

It is an amenable number.

21657869 is a deficient number, since it is larger than the sum of its proper divisors (223375).

21657869 is an equidigital number, since it uses as much as digits as its factorization.

21657869 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 223374.

The product of its digits is 181440, while the sum is 44.

The square root of 21657869 is about 4653.8015643128. The cubic root of 21657869 is about 278.7438157449.

It can be divided in two parts, 216 and 57869, that added together give a palindrome (58085).

The spelling of 21657869 in words is "twenty-one million, six hundred fifty-seven thousand, eight hundred sixty-nine".