21523561 has 8 divisors (see below), whose sum is σ = 23641920. Its totient is φ = 19503792.

The previous prime is 21523543. The next prime is 21523571. The reversal of 21523561 is 16532512.

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 21523561 - 2⁷ = 21523433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21523511) 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 7 ways as a sum of consecutive naturals, for example, 24190 + ... + 25063.

It is an arithmetic number, because the mean of its divisors is an integer number (2955240).

Almost surely, 2^21523561 is an apocalyptic number.

It is an amenable number.

21523561 is a deficient number, since it is larger than the sum of its proper divisors (2118359).

21523561 is a wasteful number, since it uses less digits than its factorization.

21523561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49295.

The product of its digits is 1800, while the sum is 25.

The square root of 21523561 is about 4639.3492000495. The cubic root of 21523561 is about 278.1664246845.

It can be divided in two parts, 215235 and 61, that added together give a square (215296 = 464²).

The spelling of 21523561 in words is "twenty-one million, five hundred twenty-three thousand, five hundred sixty-one".