21001801 has 2 divisors, whose sum is σ = 21001802. Its totient is φ = 21001800.

The previous prime is 21001781. The next prime is 21001811. The reversal of 21001801 is 10810012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12145225 + 8856576 = 3485^2 + 2976^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001801 - 2²³ = 12613193 is a prime.

It is not a weakly prime, because it can be changed into another prime (21001811) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500900 + 10500901.

It is an arithmetic number, because the mean of its divisors is an integer number (10500901).

Almost surely, 2^21001801 is an apocalyptic number.

It is an amenable number.

21001801 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001801 is an equidigital number, since it uses as much as digits as its factorization.

21001801 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16, while the sum is 13.

The square root of 21001801 is about 4582.7721959530. The cubic root of 21001801 is about 275.9003044324.

Adding to 21001801 its reverse (10810012), we get a palindrome (31811813).

The spelling of 21001801 in words is "twenty-one million, one thousand, eight hundred one".