20621001561 has 4 divisors (see below), whose sum is σ = 27494668752. Its totient is φ = 13747334372.

The previous prime is 20621001503. The next prime is 20621001589. The reversal of 20621001561 is 16510012602.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20621001561 - 2⁶ = 20621001497 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20621001161) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3436833591 + ... + 3436833596.

It is an arithmetic number, because the mean of its divisors is an integer number (6873667188).

Almost surely, 2^20621001561 is an apocalyptic number.

It is an amenable number.

20621001561 is a deficient number, since it is larger than the sum of its proper divisors (6873667191).

20621001561 is an equidigital number, since it uses as much as digits as its factorization.

20621001561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6873667190.

The product of its (nonzero) digits is 720, while the sum is 24.

The spelling of 20621001561 in words is "twenty billion, six hundred twenty-one million, one thousand, five hundred sixty-one".