21672221 has 2 divisors, whose sum is σ = 21672222. Its totient is φ = 21672220.

The previous prime is 21672191. The next prime is 21672227. The reversal of 21672221 is 12227612.

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., 15888196 + 5784025 = 3986^2 + 2405^2 .

It is a cyclic number.

It is not a de Polignac number, because 21672221 - 2¹⁰ = 21671197 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21672227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10836110 + 10836111.

It is an arithmetic number, because the mean of its divisors is an integer number (10836111).

Almost surely, 2^21672221 is an apocalyptic number.

It is an amenable number.

21672221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21672221 is an equidigital number, since it uses as much as digits as its factorization.

21672221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 672, while the sum is 23.

The square root of 21672221 is about 4655.3432741314. The cubic root of 21672221 is about 278.8053737848.

Adding to 21672221 its reverse (12227612), we get a palindrome (33899833).

It can be divided in two parts, 21 and 672221, that multiplied together give a triangular number (14116641 = T₅₃₁₃).

The spelling of 21672221 in words is "twenty-one million, six hundred seventy-two thousand, two hundred twenty-one".