21542321 has 2 divisors, whose sum is σ = 21542322. Its totient is φ = 21542320.

The previous prime is 21542299. The next prime is 21542341. The reversal of 21542321 is 12324512.

It is an a-pointer prime, because the next prime (21542341) can be obtained adding 21542321 to its sum of digits (20).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 739600 = 4561^2 + 860^2 .

It is a cyclic number.

It is not a de Polignac number, because 21542321 - 2¹⁰ = 21541297 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21542293 and 21542302.

It is not a weakly prime, because it can be changed into another prime (21542341) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10771160 + 10771161.

It is an arithmetic number, because the mean of its divisors is an integer number (10771161).

Almost surely, 2^21542321 is an apocalyptic number.

It is an amenable number.

21542321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21542321 is an equidigital number, since it uses as much as digits as its factorization.

21542321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 480, while the sum is 20.

The square root of 21542321 is about 4641.3705949859. The cubic root of 21542321 is about 278.2472181111.

Adding to 21542321 its reverse (12324512), we get a palindrome (33866833).

The spelling of 21542321 in words is "twenty-one million, five hundred forty-two thousand, three hundred twenty-one".