20720856688409 has 2 divisors, whose sum is σ = 20720856688410. Its totient is φ = 20720856688408.

The previous prime is 20720856688391. The next prime is 20720856688463. The reversal of 20720856688409 is 90488665802702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16248985186009 + 4471871502400 = 4031003^2 + 2114680^2 .

It is a cyclic number.

It is not a de Polignac number, because 20720856688409 - 2¹² = 20720856684313 is a prime.

It is a super-2 number, since 2×20720856688409² (a number of 27 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20720856688709) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360428344204 + 10360428344205.

It is an arithmetic number, because the mean of its divisors is an integer number (10360428344205).

Almost surely, 2^{20720856688409} is an apocalyptic number.

It is an amenable number.

20720856688409 is a deficient number, since it is larger than the sum of its proper divisors (1).

20720856688409 is an equidigital number, since it uses as much as digits as its factorization.

20720856688409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 92897280, while the sum is 65.

The spelling of 20720856688409 in words is "twenty trillion, seven hundred twenty billion, eight hundred fifty-six million, six hundred eighty-eight thousand, four hundred nine".