21649481 has 4 divisors (see below), whose sum is σ = 24742272. Its totient is φ = 18556692.

The previous prime is 21649447. The next prime is 21649487. The reversal of 21649481 is 18494612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21649481 - 2¹⁸ = 21387337 is a prime.

It is a super-2 number, since 2×21649481² = 937400055138722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21649487) 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, 1546385 + ... + 1546398.

It is an arithmetic number, because the mean of its divisors is an integer number (6185568).

Almost surely, 2^21649481 is an apocalyptic number.

It is an amenable number.

21649481 is a deficient number, since it is larger than the sum of its proper divisors (3092791).

21649481 is an equidigital number, since it uses as much as digits as its factorization.

21649481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3092790.

The product of its digits is 13824, while the sum is 35.

The square root of 21649481 is about 4652.9002783210. The cubic root of 21649481 is about 278.7078256691.

The spelling of 21649481 in words is "twenty-one million, six hundred forty-nine thousand, four hundred eighty-one".