21605028208817 has 2 divisors, whose sum is σ = 21605028208818. Its totient is φ = 21605028208816.

The previous prime is 21605028208711. The next prime is 21605028208837. The reversal of 21605028208817 is 71880282050612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17157522602896 + 4447505605921 = 4142164^2 + 2108911^2 .

It is a cyclic number.

It is not a de Polignac number, because 21605028208817 - 2²² = 21605024014513 is a prime.

It is not a weakly prime, because it can be changed into another prime (21605028208837) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802514104408 + 10802514104409.

It is an arithmetic number, because the mean of its divisors is an integer number (10802514104409).

Almost surely, 2^{21605028208817} is an apocalyptic number.

It is an amenable number.

21605028208817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21605028208817 is an equidigital number, since it uses as much as digits as its factorization.

21605028208817 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 860160, while the sum is 50.

The spelling of 21605028208817 in words is "twenty-one trillion, six hundred five billion, twenty-eight million, two hundred eight thousand, eight hundred seventeen".