20561621178 has 48 divisors (see below), whose sum is σ = 47908782720. Its totient is φ = 5865963264.

The previous prime is 20561621173. The next prime is 20561621189. The reversal of 20561621178 is 87112616502.

It is not an unprimeable number, because it can be changed into a prime (20561621173) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 145903 + ... + 249821.

It is an arithmetic number, because the mean of its divisors is an integer number (998099640).

Almost surely, 2^20561621178 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20561621178, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23954391360).

20561621178 is an abundant number, since it is smaller than the sum of its proper divisors (27347161542).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20561621178 is a wasteful number, since it uses less digits than its factorization.

20561621178 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104611 (or 104604 counting only the distinct ones).

The product of its (nonzero) digits is 40320, while the sum is 39.

The spelling of 20561621178 in words is "twenty billion, five hundred sixty-one million, six hundred twenty-one thousand, one hundred seventy-eight".