21088421 has 2 divisors, whose sum is σ = 21088422. Its totient is φ = 21088420.

The previous prime is 21088393. The next prime is 21088439. The reversal of 21088421 is 12488012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17757796 + 3330625 = 4214^2 + 1825^2 .

It is a cyclic number.

It is not a de Polignac number, because 21088421 - 2⁶ = 21088357 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21088321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10544210 + 10544211.

It is an arithmetic number, because the mean of its divisors is an integer number (10544211).

Almost surely, 2^21088421 is an apocalyptic number.

It is an amenable number.

21088421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21088421 is an equidigital number, since it uses as much as digits as its factorization.

21088421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 21088421 is about 4592.2130830352. The cubic root of 21088421 is about 276.2790926412.

The spelling of 21088421 in words is "twenty-one million, eighty-eight thousand, four hundred twenty-one".