21604481 has 2 divisors, whose sum is σ = 21604482. Its totient is φ = 21604480.

The previous prime is 21604469. The next prime is 21604487. The reversal of 21604481 is 18440612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21307456 + 297025 = 4616^2 + 545^2 .

It is a cyclic number.

It is not a de Polignac number, because 21604481 - 2¹⁴ = 21588097 is a prime.

It is a super-2 number, since 2×21604481² = 933507198558722, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21604481.

It is not a weakly prime, because it can be changed into another prime (21604487) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802240 + 10802241.

It is an arithmetic number, because the mean of its divisors is an integer number (10802241).

Almost surely, 2^21604481 is an apocalyptic number.

It is an amenable number.

21604481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604481 is an equidigital number, since it uses as much as digits as its factorization.

21604481 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1536, while the sum is 26.

The square root of 21604481 is about 4648.0620692930. The cubic root of 21604481 is about 278.5145869811.

The spelling of 21604481 in words is "twenty-one million, six hundred four thousand, four hundred eighty-one".