21381457 has 2 divisors, whose sum is σ = 21381458. Its totient is φ = 21381456.

The previous prime is 21381433. The next prime is 21381469. The reversal of 21381457 is 75418312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21381376 + 81 = 4624^2 + 9^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21381457 is a prime.

It is not a weakly prime, because it can be changed into another prime (21381407) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690728 + 10690729.

It is an arithmetic number, because the mean of its divisors is an integer number (10690729).

Almost surely, 2^21381457 is an apocalyptic number.

It is an amenable number.

21381457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21381457 is an equidigital number, since it uses as much as digits as its factorization.

21381457 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6720, while the sum is 31.

The square root of 21381457 is about 4624.0087586422. The cubic root of 21381457 is about 277.5528974181.

Adding to 21381457 its reverse (75418312), we get a palindrome (96799769).

The spelling of 21381457 in words is "twenty-one million, three hundred eighty-one thousand, four hundred fifty-seven".