21643481 has 4 divisors (see below), whose sum is σ = 21666612. Its totient is φ = 21620352.

The previous prime is 21643429. The next prime is 21643507. The reversal of 21643481 is 18434612.

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 10621081 + 11022400 = 3259^2 + 3320^2 .

It is a cyclic number.

It is not a de Polignac number, because 21643481 - 2¹⁰ = 21642457 is a prime.

It is a super-2 number, since 2×21643481² = 936880539594722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21643411) 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, 10100 + ... + 12053.

It is an arithmetic number, because the mean of its divisors is an integer number (5416653).

Almost surely, 2^21643481 is an apocalyptic number.

It is an amenable number.

21643481 is a deficient number, since it is larger than the sum of its proper divisors (23131).

21643481 is an equidigital number, since it uses as much as digits as its factorization.

21643481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23130.

The product of its digits is 4608, while the sum is 29.

The square root of 21643481 is about 4652.2554744984. The cubic root of 21643481 is about 278.6820759916.

The spelling of 21643481 in words is "twenty-one million, six hundred forty-three thousand, four hundred eighty-one".