20665315621 has 2 divisors, whose sum is σ = 20665315622. Its totient is φ = 20665315620.

The previous prime is 20665315603. The next prime is 20665315669. The reversal of 20665315621 is 12651356602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18587232225 + 2078083396 = 136335^2 + 45586^2 .

It is a cyclic number.

It is not a de Polignac number, because 20665315621 - 2⁵ = 20665315589 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20665312621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10332657810 + 10332657811.

It is an arithmetic number, because the mean of its divisors is an integer number (10332657811).

Almost surely, 2^20665315621 is an apocalyptic number.

It is an amenable number.

20665315621 is a deficient number, since it is larger than the sum of its proper divisors (1).

20665315621 is an equidigital number, since it uses as much as digits as its factorization.

20665315621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 64800, while the sum is 37.

The spelling of 20665315621 in words is "twenty billion, six hundred sixty-five million, three hundred fifteen thousand, six hundred twenty-one".