21635641 has 2 divisors, whose sum is σ = 21635642. Its totient is φ = 21635640.

The previous prime is 21635609. The next prime is 21635657. The reversal of 21635641 is 14653612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15405625 + 6230016 = 3925^2 + 2496^2 .

It is a cyclic number.

It is not a de Polignac number, because 21635641 - 2⁵ = 21635609 is a prime.

It is a super-2 number, since 2×21635641² = 936201922961762, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21635671) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10817820 + 10817821.

It is an arithmetic number, because the mean of its divisors is an integer number (10817821).

Almost surely, 2^21635641 is an apocalyptic number.

It is an amenable number.

21635641 is a deficient number, since it is larger than the sum of its proper divisors (1).

21635641 is an equidigital number, since it uses as much as digits as its factorization.

21635641 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 28.

The square root of 21635641 is about 4651.4127961298. The cubic root of 21635641 is about 278.6484225736.

The spelling of 21635641 in words is "twenty-one million, six hundred thirty-five thousand, six hundred forty-one".