21604505261 has 2 divisors, whose sum is σ = 21604505262. Its totient is φ = 21604505260.

The previous prime is 21604505257. The next prime is 21604505287. The reversal of 21604505261 is 16250540612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12408846025 + 9195659236 = 111395^2 + 95894^2 .

It is a cyclic number.

It is not a de Polignac number, because 21604505261 - 2² = 21604505257 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21604105261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802252630 + 10802252631.

It is an arithmetic number, because the mean of its divisors is an integer number (10802252631).

Almost surely, 2^21604505261 is an apocalyptic number.

It is an amenable number.

21604505261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604505261 is an equidigital number, since it uses as much as digits as its factorization.

21604505261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14400, while the sum is 32.

The spelling of 21604505261 in words is "twenty-one billion, six hundred four million, five hundred five thousand, two hundred sixty-one".