21557287 has 2 divisors, whose sum is σ = 21557288. Its totient is φ = 21557286.

The previous prime is 21557251. The next prime is 21557293. The reversal of 21557287 is 78275512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21557287 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21557387) 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 as a sum of consecutive naturals, namely, 10778643 + 10778644.

It is an arithmetic number, because the mean of its divisors is an integer number (10778644).

Almost surely, 2^21557287 is an apocalyptic number.

21557287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557287 is an equidigital number, since it uses as much as digits as its factorization.

21557287 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 39200, while the sum is 37.

The square root of 21557287 is about 4642.9825543502. The cubic root of 21557287 is about 278.3116383423.

The spelling of 21557287 in words is "twenty-one million, five hundred fifty-seven thousand, two hundred eighty-seven".