21608708021 has 2 divisors, whose sum is σ = 21608708022. Its totient is φ = 21608708020.

The previous prime is 21608708003. The next prime is 21608708057. The reversal of 21608708021 is 12080780612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21282724996 + 325983025 = 145886^2 + 18055^2 .

It is a cyclic number.

It is not a de Polignac number, because 21608708021 - 2¹⁰ = 21608706997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21608708521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10804354010 + 10804354011.

It is an arithmetic number, because the mean of its divisors is an integer number (10804354011).

Almost surely, 2^21608708021 is an apocalyptic number.

It is an amenable number.

21608708021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21608708021 is an equidigital number, since it uses as much as digits as its factorization.

21608708021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10752, while the sum is 35.

The spelling of 21608708021 in words is "twenty-one billion, six hundred eight million, seven hundred eight thousand, twenty-one".