21165650021 has 2 divisors, whose sum is σ = 21165650022. Its totient is φ = 21165650020.

The previous prime is 21165649979. The next prime is 21165650027. The reversal of 21165650021 is 12005656112.

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., 14590224100 + 6575425921 = 120790^2 + 81089^2 .

It is a cyclic number.

It is not a de Polignac number, because 21165650021 - 2¹⁰ = 21165648997 is a prime.

It is a super-2 number, since 2×21165650021² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21165650027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10582825010 + 10582825011.

It is an arithmetic number, because the mean of its divisors is an integer number (10582825011).

Almost surely, 2^21165650021 is an apocalyptic number.

It is an amenable number.

21165650021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21165650021 is an equidigital number, since it uses as much as digits as its factorization.

21165650021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3600, while the sum is 29.

The spelling of 21165650021 in words is "twenty-one billion, one hundred sixty-five million, six hundred fifty thousand, twenty-one".