21123309997 has 2 divisors, whose sum is σ = 21123309998. Its totient is φ = 21123309996.

The previous prime is 21123309973. The next prime is 21123310037. The reversal of 21123309997 is 79990332112.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17929477801 + 3193832196 = 133901^2 + 56514^2 .

It is a cyclic number.

It is not a de Polignac number, because 21123309997 - 2¹⁵ = 21123277229 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123309947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561654998 + 10561654999.

It is an arithmetic number, because the mean of its divisors is an integer number (10561654999).

Almost surely, 2^21123309997 is an apocalyptic number.

It is an amenable number.

21123309997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123309997 is an equidigital number, since it uses as much as digits as its factorization.

21123309997 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 183708, while the sum is 46.

The spelling of 21123309997 in words is "twenty-one billion, one hundred twenty-three million, three hundred nine thousand, nine hundred ninety-seven".