21636481 has 4 divisors (see below), whose sum is σ = 22334464. Its totient is φ = 20938500.

The previous prime is 21636473. The next prime is 21636487. The reversal of 21636481 is 18463612.

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 a cyclic number.

It is not a de Polignac number, because 21636481 - 2³ = 21636473 is a prime.

It is a super-2 number, since 2×21636481² = 936274620126722, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 697951 = 21636481 / (2 + 1 + 6 + 3 + 6 + 4 + 8 + 1).

It is a Duffinian number.

It is a plaindrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (21636487) 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, 348945 + ... + 349006.

It is an arithmetic number, because the mean of its divisors is an integer number (5583616).

Almost surely, 2^21636481 is an apocalyptic number.

It is an amenable number.

21636481 is a deficient number, since it is larger than the sum of its proper divisors (697983).

21636481 is an equidigital number, since it uses as much as digits as its factorization.

21636481 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 697982.

The product of its digits is 6912, while the sum is 31.

The square root of 21636481 is about 4651.5030903999. The cubic root of 21636481 is about 278.6520286858.

The spelling of 21636481 in words is "twenty-one million, six hundred thirty-six thousand, four hundred eighty-one".