21004402261 has 2 divisors, whose sum is σ = 21004402262. Its totient is φ = 21004402260.

The previous prime is 21004402231. The next prime is 21004402271. The reversal of 21004402261 is 16220440012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14890100625 + 6114301636 = 122025^2 + 78194^2 .

It is a cyclic number.

It is not a de Polignac number, because 21004402261 - 2⁵ = 21004402229 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21004402231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502201130 + 10502201131.

It is an arithmetic number, because the mean of its divisors is an integer number (10502201131).

Almost surely, 2^21004402261 is an apocalyptic number.

It is an amenable number.

21004402261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21004402261 is an equidigital number, since it uses as much as digits as its factorization.

21004402261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 768, while the sum is 22.

Adding to 21004402261 its reverse (16220440012), we get a palindrome (37224842273).

The spelling of 21004402261 in words is "twenty-one billion, four million, four hundred two thousand, two hundred sixty-one".