21101100661 has 2 divisors, whose sum is σ = 21101100662. Its totient is φ = 21101100660.

The previous prime is 21101100649. The next prime is 21101100701. The reversal of 21101100661 is 16600110112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21097562500 + 3538161 = 145250^2 + 1881^2 .

It is a cyclic number.

It is not a de Polignac number, because 21101100661 - 2⁹ = 21101100149 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21101100061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10550550330 + 10550550331.

It is an arithmetic number, because the mean of its divisors is an integer number (10550550331).

Almost surely, 2^21101100661 is an apocalyptic number.

It is an amenable number.

21101100661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21101100661 is an equidigital number, since it uses as much as digits as its factorization.

21101100661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 72, while the sum is 19.

Adding to 21101100661 its reverse (16600110112), we get a palindrome (37701210773).

The spelling of 21101100661 in words is "twenty-one billion, one hundred one million, one hundred thousand, six hundred sixty-one".