21801553 has 2 divisors, whose sum is σ = 21801554. Its totient is φ = 21801552.

The previous prime is 21801517. The next prime is 21801581. The reversal of 21801553 is 35510812.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20684304 + 1117249 = 4548^2 + 1057^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21801553 is a prime.

It is not a weakly prime, because it can be changed into another prime (21801653) 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, 10900776 + 10900777.

It is an arithmetic number, because the mean of its divisors is an integer number (10900777).

Almost surely, 2^21801553 is an apocalyptic number.

It is an amenable number.

21801553 is a deficient number, since it is larger than the sum of its proper divisors (1).

21801553 is an equidigital number, since it uses as much as digits as its factorization.

21801553 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1200, while the sum is 25.

The square root of 21801553 is about 4669.2133170375. The cubic root of 21801553 is about 279.3588775152.

The spelling of 21801553 in words is "twenty-one million, eight hundred one thousand, five hundred fifty-three".