21620687749 has 2 divisors, whose sum is σ = 21620687750. Its totient is φ = 21620687748.

The previous prime is 21620687731. The next prime is 21620687773. The reversal of 21620687749 is 94778602612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12361437124 + 9259250625 = 111182^2 + 96225^2 .

It is a cyclic number.

It is not a de Polignac number, because 21620687749 - 2²⁵ = 21587133317 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21620687696 and 21620687705.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21620687719) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810343874 + 10810343875.

It is an arithmetic number, because the mean of its divisors is an integer number (10810343875).

Almost surely, 2^21620687749 is an apocalyptic number.

It is an amenable number.

21620687749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21620687749 is an equidigital number, since it uses as much as digits as its factorization.

21620687749 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2032128, while the sum is 52.

The spelling of 21620687749 in words is "twenty-one billion, six hundred twenty million, six hundred eighty-seven thousand, seven hundred forty-nine".