21557289 has 8 divisors (see below), whose sum is σ = 30954112. Its totient is φ = 13266000.

The previous prime is 21557287. The next prime is 21557293. The reversal of 21557289 is 98275512.

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

It is not a de Polignac number, because 21557289 - 2¹ = 21557287 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39), and also a Moran number because the ratio is a prime number: 552751 = 21557289 / (2 + 1 + 5 + 5 + 7 + 2 + 8 + 9).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21557287) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 276337 + ... + 276414.

It is an arithmetic number, because the mean of its divisors is an integer number (3869264).

Almost surely, 2^21557289 is an apocalyptic number.

It is an amenable number.

21557289 is a deficient number, since it is larger than the sum of its proper divisors (9396823).

21557289 is a wasteful number, since it uses less digits than its factorization.

21557289 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 552767.

The product of its digits is 50400, while the sum is 39.

The square root of 21557289 is about 4642.9827697290. The cubic root of 21557289 is about 278.3116469492.

The spelling of 21557289 in words is "twenty-one million, five hundred fifty-seven thousand, two hundred eighty-nine".