21553421 has 2 divisors, whose sum is σ = 21553422. Its totient is φ = 21553420.

The previous prime is 21553417. The next prime is 21553453. The reversal of 21553421 is 12435512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20376196 + 1177225 = 4514^2 + 1085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21553421 - 2² = 21553417 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 (21553481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10776710 + 10776711.

It is an arithmetic number, because the mean of its divisors is an integer number (10776711).

Almost surely, 2^21553421 is an apocalyptic number.

It is an amenable number.

21553421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21553421 is an equidigital number, since it uses as much as digits as its factorization.

21553421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 23.

The square root of 21553421 is about 4642.5662084670. The cubic root of 21553421 is about 278.2950002388.

Adding to 21553421 its reverse (12435512), we get a palindrome (33988933).

The spelling of 21553421 in words is "twenty-one million, five hundred fifty-three thousand, four hundred twenty-one".