21661233 has 16 divisors (see below), whose sum is σ = 31708416. Its totient is φ = 13044240.

The previous prime is 21661223. The next prime is 21661253. The reversal of 21661233 is 33216612.

It is a happy number.

It is not a de Polignac number, because 21661233 - 2¹² = 21657137 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21661223) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3366 + ... + 7392.

It is an arithmetic number, because the mean of its divisors is an integer number (1981776).

Almost surely, 2^21661233 is an apocalyptic number.

It is an amenable number.

21661233 is a deficient number, since it is larger than the sum of its proper divisors (10047183).

21661233 is a wasteful number, since it uses less digits than its factorization.

21661233 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4204.

The product of its digits is 1296, while the sum is 24.

The square root of 21661233 is about 4654.1629752298. The cubic root of 21661233 is about 278.7582469223.

Adding to 21661233 its reverse (33216612), we get a palindrome (54877845).

The spelling of 21661233 in words is "twenty-one million, six hundred sixty-one thousand, two hundred thirty-three".