21629561 has 2 divisors, whose sum is σ = 21629562. Its totient is φ = 21629560.

The previous prime is 21629557. The next prime is 21629579. The reversal of 21629561 is 16592612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14100025 + 7529536 = 3755^2 + 2744^2 .

It is a cyclic number.

It is not a de Polignac number, because 21629561 - 2² = 21629557 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a plaindrome in base 11.

It is not a weakly prime, because it can be changed into another prime (21629501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10814780 + 10814781.

It is an arithmetic number, because the mean of its divisors is an integer number (10814781).

Almost surely, 2^21629561 is an apocalyptic number.

It is an amenable number.

21629561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21629561 is an equidigital number, since it uses as much as digits as its factorization.

21629561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 32.

The square root of 21629561 is about 4650.7591853374. The cubic root of 21629561 is about 278.6223184070.

The spelling of 21629561 in words is "twenty-one million, six hundred twenty-nine thousand, five hundred sixty-one".