20478611561 has 2 divisors, whose sum is σ = 20478611562. Its totient is φ = 20478611560.

The previous prime is 20478611557. The next prime is 20478611623. The reversal of 20478611561 is 16511687402.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17867401561 + 2611210000 = 133669^2 + 51100^2 .

It is a cyclic number.

It is not a de Polignac number, because 20478611561 - 2² = 20478611557 is a prime.

It is not a weakly prime, because it can be changed into another prime (20478611861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10239305780 + 10239305781.

It is an arithmetic number, because the mean of its divisors is an integer number (10239305781).

Almost surely, 2^20478611561 is an apocalyptic number.

It is an amenable number.

20478611561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20478611561 is an equidigital number, since it uses as much as digits as its factorization.

20478611561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 80640, while the sum is 41.

The spelling of 20478611561 in words is "twenty billion, four hundred seventy-eight million, six hundred eleven thousand, five hundred sixty-one".