20665215121 has 2 divisors, whose sum is σ = 20665215122. Its totient is φ = 20665215120.

The previous prime is 20665215089. The next prime is 20665215139. The reversal of 20665215121 is 12151256602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14528686225 + 6136528896 = 120535^2 + 78336^2 .

It is a cyclic number.

It is not a de Polignac number, because 20665215121 - 2⁵ = 20665215089 is a prime.

It is a super-2 number, since 2×20665215121² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20665215161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10332607560 + 10332607561.

It is an arithmetic number, because the mean of its divisors is an integer number (10332607561).

Almost surely, 2^20665215121 is an apocalyptic number.

It is an amenable number.

20665215121 is a deficient number, since it is larger than the sum of its proper divisors (1).

20665215121 is an equidigital number, since it uses as much as digits as its factorization.

20665215121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7200, while the sum is 31.

The spelling of 20665215121 in words is "twenty billion, six hundred sixty-five million, two hundred fifteen thousand, one hundred twenty-one".