20621245781 has 2 divisors, whose sum is σ = 20621245782. Its totient is φ = 20621245780.

The previous prime is 20621245763. The next prime is 20621245783. The reversal of 20621245781 is 18754212602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17064196900 + 3557048881 = 130630^2 + 59641^2 .

It is a cyclic number.

It is not a de Polignac number, because 20621245781 - 2⁶ = 20621245717 is a prime.

It is a super-2 number, since 2×20621245781² (a number of 21 digits) contains 22 as substring.

Together with 20621245783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20621245783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10310622890 + 10310622891.

It is an arithmetic number, because the mean of its divisors is an integer number (10310622891).

Almost surely, 2^20621245781 is an apocalyptic number.

It is an amenable number.

20621245781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20621245781 is an equidigital number, since it uses as much as digits as its factorization.

20621245781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 53760, while the sum is 38.

The spelling of 20621245781 in words is "twenty billion, six hundred twenty-one million, two hundred forty-five thousand, seven hundred eighty-one".