21818557 has 2 divisors, whose sum is σ = 21818558. Its totient is φ = 21818556.

The previous prime is 21818539. The next prime is 21818561. The reversal of 21818557 is 75581812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21724921 + 93636 = 4661^2 + 306^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21818557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21818507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10909278 + 10909279.

It is an arithmetic number, because the mean of its divisors is an integer number (10909279).

Almost surely, 2^21818557 is an apocalyptic number.

It is an amenable number.

21818557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21818557 is an equidigital number, since it uses as much as digits as its factorization.

21818557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 22400, while the sum is 37.

The square root of 21818557 is about 4671.0338256108. The cubic root of 21818557 is about 279.4314867756.

The spelling of 21818557 in words is "twenty-one million, eight hundred eighteen thousand, five hundred fifty-seven".