21209633 has 2 divisors, whose sum is σ = 21209634. Its totient is φ = 21209632.

The previous prime is 21209623. The next prime is 21209653. The reversal of 21209633 is 33690212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15864289 + 5345344 = 3983^2 + 2312^2 .

It is a cyclic number.

It is not a de Polignac number, because 21209633 - 2²² = 17015329 is a prime.

It is not a weakly prime, because it can be changed into another prime (21209603) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10604816 + 10604817.

It is an arithmetic number, because the mean of its divisors is an integer number (10604817).

Almost surely, 2^21209633 is an apocalyptic number.

It is an amenable number.

21209633 is a deficient number, since it is larger than the sum of its proper divisors (1).

21209633 is an equidigital number, since it uses as much as digits as its factorization.

21209633 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1944, while the sum is 26.

The square root of 21209633 is about 4605.3917314383. The cubic root of 21209633 is about 276.8074139106.

Adding to 21209633 its reverse (33690212), we get a palindrome (54899845).

The spelling of 21209633 in words is "twenty-one million, two hundred nine thousand, six hundred thirty-three".