21558001 has 2 divisors, whose sum is σ = 21558002. Its totient is φ = 21558000.

The previous prime is 21557983. The next prime is 21558037. The reversal of 21558001 is 10085512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20711601 + 846400 = 4551^2 + 920^2 .

It is a cyclic number.

It is not a de Polignac number, because 21558001 - 2¹⁷ = 21426929 is a prime.

It is not a weakly prime, because it can be changed into another prime (21558041) 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 as a sum of consecutive naturals, namely, 10779000 + 10779001.

It is an arithmetic number, because the mean of its divisors is an integer number (10779001).

Almost surely, 2^21558001 is an apocalyptic number.

It is an amenable number.

21558001 is a deficient number, since it is larger than the sum of its proper divisors (1).

21558001 is an equidigital number, since it uses as much as digits as its factorization.

21558001 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 400, while the sum is 22.

The square root of 21558001 is about 4643.0594439443. The cubic root of 21558001 is about 278.3147109664.

The spelling of 21558001 in words is "twenty-one million, five hundred fifty-eight thousand, one".