21611221 has 2 divisors, whose sum is σ = 21611222. Its totient is φ = 21611220.

The previous prime is 21611203. The next prime is 21611231. The reversal of 21611221 is 12211612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16112196 + 5499025 = 4014^2 + 2345^2 .

It is a cyclic number.

It is not a de Polignac number, because 21611221 - 2²¹ = 19514069 is a prime.

It is a super-2 number, since 2×21611221² = 934089746221682, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21611195 and 21611204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21611231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805610 + 10805611.

It is an arithmetic number, because the mean of its divisors is an integer number (10805611).

Almost surely, 2^21611221 is an apocalyptic number.

It is an amenable number.

21611221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611221 is an equidigital number, since it uses as much as digits as its factorization.

21611221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48, while the sum is 16.

The square root of 21611221 is about 4648.7870461014. The cubic root of 21611221 is about 278.5435469167.

Adding to 21611221 its reverse (12211612), we get a palindrome (33822833).

The spelling of 21611221 in words is "twenty-one million, six hundred eleven thousand, two hundred twenty-one".