21400381 has 2 divisors, whose sum is σ = 21400382. Its totient is φ = 21400380.

The previous prime is 21400367. The next prime is 21400387. The reversal of 21400381 is 18300412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15920100 + 5480281 = 3990^2 + 2341^2 .

It is a cyclic number.

It is not a de Polignac number, because 21400381 - 2¹⁵ = 21367613 is a prime.

It is a super-2 number, since 2×21400381² = 915952613890322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21400387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10700190 + 10700191.

It is an arithmetic number, because the mean of its divisors is an integer number (10700191).

Almost surely, 2^21400381 is an apocalyptic number.

It is an amenable number.

21400381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21400381 is an equidigital number, since it uses as much as digits as its factorization.

21400381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 21400381 is about 4626.0545824709. The cubic root of 21400381 is about 277.6347574805.

Adding to 21400381 its reverse (18300412), we get a palindrome (39700793).

The spelling of 21400381 in words is "twenty-one million, four hundred thousand, three hundred eighty-one".