21400397 has 2 divisors, whose sum is σ = 21400398. Its totient is φ = 21400396.

The previous prime is 21400387. The next prime is 21400417. The reversal of 21400397 is 79300412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16859236 + 4541161 = 4106^2 + 2131^2 .

It is a cyclic number.

It is not a de Polignac number, because 21400397 - 2⁴ = 21400381 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21400367) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10700198 + 10700199.

It is an arithmetic number, because the mean of its divisors is an integer number (10700199).

Almost surely, 2^21400397 is an apocalyptic number.

It is an amenable number.

21400397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21400397 is an equidigital number, since it uses as much as digits as its factorization.

21400397 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1512, while the sum is 26.

The square root of 21400397 is about 4626.0563118060. The cubic root of 21400397 is about 277.6348266717.

The spelling of 21400397 in words is "twenty-one million, four hundred thousand, three hundred ninety-seven".