21712561 has 8 divisors (see below), whose sum is σ = 24189480. Its totient is φ = 19350912.

The previous prime is 21712541. The next prime is 21712567. The reversal of 21712561 is 16521712.

It can be written as a sum of positive squares in 4 ways, for example, as 34225 + 21678336 = 185^2 + 4656^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21712561 - 2¹³ = 21704369 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21712567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28420 + ... + 29173.

It is an arithmetic number, because the mean of its divisors is an integer number (3023685).

Almost surely, 2^21712561 is an apocalyptic number.

It is an amenable number.

21712561 is a deficient number, since it is larger than the sum of its proper divisors (2476919).

21712561 is a wasteful number, since it uses less digits than its factorization.

21712561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57635.

The product of its digits is 840, while the sum is 25.

The square root of 21712561 is about 4659.6739156297. The cubic root of 21712561 is about 278.9782531235.

The spelling of 21712561 in words is "twenty-one million, seven hundred twelve thousand, five hundred sixty-one".