21611621 has 2 divisors, whose sum is σ = 21611622. Its totient is φ = 21611620.

The previous prime is 21611617. The next prime is 21611669. The reversal of 21611621 is 12611612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20205025 + 1406596 = 4495^2 + 1186^2 .

It is a cyclic number.

It is not a de Polignac number, because 21611621 - 2² = 21611617 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21611593 and 21611602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21611221) 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, 10805810 + 10805811.

It is an arithmetic number, because the mean of its divisors is an integer number (10805811).

Almost surely, 2^21611621 is an apocalyptic number.

It is an amenable number.

21611621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611621 is an equidigital number, since it uses as much as digits as its factorization.

21611621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 144, while the sum is 20.

The square root of 21611621 is about 4648.8300678773. The cubic root of 21611621 is about 278.5452654180.

Subtracting from 21611621 its reverse (12611612), we obtain a palindrome (9000009).

The spelling of 21611621 in words is "twenty-one million, six hundred eleven thousand, six hundred twenty-one".