21278401 has 2 divisors, whose sum is σ = 21278402. Its totient is φ = 21278400.

The previous prime is 21278399. The next prime is 21278417. The reversal of 21278401 is 10487212.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15397776 + 5880625 = 3924^2 + 2425^2 .

It is a cyclic number.

It is not a de Polignac number, because 21278401 - 2¹ = 21278399 is a prime.

Together with 21278399, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21278471) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10639200 + 10639201.

It is an arithmetic number, because the mean of its divisors is an integer number (10639201).

Almost surely, 2^21278401 is an apocalyptic number.

It is an amenable number.

21278401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21278401 is an equidigital number, since it uses as much as digits as its factorization.

21278401 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21278401 is about 4612.8517210073. The cubic root of 21278401 is about 277.1062554212.

The spelling of 21278401 in words is "twenty-one million, two hundred seventy-eight thousand, four hundred one".