20917561 has 6 divisors (see below), whose sum is σ = 24332730. Its totient is φ = 17929296.

The previous prime is 20917553. The next prime is 20917597. The reversal of 20917561 is 16571902.

It can be written as a sum of positive squares in only one way, i.e., 11431161 + 9486400 = 3381^2 + 3080^2 .

It is not a de Polignac number, because 20917561 - 2³ = 20917553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20917661) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 213396 + ... + 213493.

It is an arithmetic number, because the mean of its divisors is an integer number (4055455).

Almost surely, 2^20917561 is an apocalyptic number.

It is an amenable number.

20917561 is a deficient number, since it is larger than the sum of its proper divisors (3415169).

20917561 is an equidigital number, since it uses as much as digits as its factorization.

20917561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 426903 (or 426896 counting only the distinct ones).

The product of its (nonzero) digits is 3780, while the sum is 31.

The square root of 20917561 is about 4573.5720175810. The cubic root of 20917561 is about 275.5309236338.

The spelling of 20917561 in words is "twenty million, nine hundred seventeen thousand, five hundred sixty-one".