21736561 has 16 divisors (see below), whose sum is σ = 27335808. Its totient is φ = 16930320.

The previous prime is 21736537. The next prime is 21736577. The reversal of 21736561 is 16563712.

It is not a de Polignac number, because 21736561 - 2⁵ = 21736529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21736661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8151 + ... + 10483.

It is an arithmetic number, because the mean of its divisors is an integer number (1708488).

Almost surely, 2^21736561 is an apocalyptic number.

It is an amenable number.

21736561 is a deficient number, since it is larger than the sum of its proper divisors (5599247).

21736561 is an equidigital number, since it uses as much as digits as its factorization.

21736561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2373 (or 2351 counting only the distinct ones).

The product of its digits is 7560, while the sum is 31.

The square root of 21736561 is about 4662.2484918760. The cubic root of 21736561 is about 279.0810048999.

The spelling of 21736561 in words is "twenty-one million, seven hundred thirty-six thousand, five hundred sixty-one".