20091561 has 16 divisors (see below), whose sum is σ = 30987264. Its totient is φ = 11341584.

The previous prime is 20091559. The next prime is 20091587. The reversal of 20091561 is 16519002.

It is not a de Polignac number, because 20091561 - 2¹ = 20091559 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20091541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4021 + ... + 7506.

It is an arithmetic number, because the mean of its divisors is an integer number (1936704).

Almost surely, 2^20091561 is an apocalyptic number.

20091561 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20091561 is a deficient number, since it is larger than the sum of its proper divisors (10895703).

20091561 is a wasteful number, since it uses less digits than its factorization.

20091561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11620.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 20091561 is about 4482.3610965651. The cubic root of 20091561 is about 271.8553558009.

It can be divided in two parts, 2009 and 1561, that added together give a triangular number (3570 = T₈₄).

The spelling of 20091561 in words is "twenty million, ninety-one thousand, five hundred sixty-one".