21278591 has 2 divisors, whose sum is σ = 21278592. Its totient is φ = 21278590.

The previous prime is 21278581. The next prime is 21278633. The reversal of 21278591 is 19587212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21278591 - 2¹⁰ = 21277567 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21278501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10639295 + 10639296.

It is an arithmetic number, because the mean of its divisors is an integer number (10639296).

Almost surely, 2^21278591 is an apocalyptic number.

21278591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21278591 is an equidigital number, since it uses as much as digits as its factorization.

21278591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10080, while the sum is 35.

The square root of 21278591 is about 4612.8723155969. The cubic root of 21278591 is about 277.1070802017.

The spelling of 21278591 in words is "twenty-one million, two hundred seventy-eight thousand, five hundred ninety-one".