20621555561 has 2 divisors, whose sum is σ = 20621555562. Its totient is φ = 20621555560.

The previous prime is 20621555527. The next prime is 20621555587. The reversal of 20621555561 is 16555512602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17460979600 + 3160575961 = 132140^2 + 56219^2 .

It is a cyclic number.

It is not a de Polignac number, because 20621555561 - 2⁶ = 20621555497 is a prime.

It is not a weakly prime, because it can be changed into another prime (20621555261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10310777780 + 10310777781.

It is an arithmetic number, because the mean of its divisors is an integer number (10310777781).

Almost surely, 2^20621555561 is an apocalyptic number.

It is an amenable number.

20621555561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20621555561 is an equidigital number, since it uses as much as digits as its factorization.

20621555561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 90000, while the sum is 38.

The spelling of 20621555561 in words is "twenty billion, six hundred twenty-one million, five hundred fifty-five thousand, five hundred sixty-one".