21749261 has 4 divisors (see below), whose sum is σ = 21758652. Its totient is φ = 21739872.

The previous prime is 21749251. The next prime is 21749269. The reversal of 21749261 is 16294712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 7873636 + 13875625 = 2806^2 + 3725^2 .

It is a cyclic number.

It is not a de Polignac number, because 21749261 - 2¹⁸ = 21487117 is a prime.

It is a super-2 number, since 2×21749261² = 946060708092242, 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 (21749269) 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, 1535 + ... + 6771.

It is an arithmetic number, because the mean of its divisors is an integer number (5439663).

Almost surely, 2^21749261 is an apocalyptic number.

It is an amenable number.

21749261 is a deficient number, since it is larger than the sum of its proper divisors (9391).

21749261 is an equidigital number, since it uses as much as digits as its factorization.

21749261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9390.

The product of its digits is 6048, while the sum is 32.

The square root of 21749261 is about 4663.6102967551. The cubic root of 21749261 is about 279.1353471163.

The spelling of 21749261 in words is "twenty-one million, seven hundred forty-nine thousand, two hundred sixty-one".