20615503561 has 9 divisors (see below), whose sum is σ = 20937560301. Its totient is φ = 20298333132.

The previous prime is 20615503553. The next prime is 20615503583. The reversal of 20615503561 is 16530551602.

The square root of 20615503561 is 143581.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 20615503561 - 2³ = 20615503553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20615503511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 9618856 + ... + 9620998.

It is an arithmetic number, because the mean of its divisors is an integer number (2326395589).

Almost surely, 2^20615503561 is an apocalyptic number.

20615503561 is the 143581-st square number.

20615503561 is the 71791-st centered octagonal number.

It is an amenable number.

20615503561 is a deficient number, since it is larger than the sum of its proper divisors (322056740).

20615503561 is an frugal number, since it uses more digits than its factorization.

20615503561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4420 (or 2210 counting only the distinct ones).

The product of its (nonzero) digits is 27000, while the sum is 34.

It can be divided in two parts, 20615 and 503561, that added together give a square (524176 = 724²).

The spelling of 20615503561 in words is "twenty billion, six hundred fifteen million, five hundred three thousand, five hundred sixty-one".