21420397 has 2 divisors, whose sum is σ = 21420398. Its totient is φ = 21420396.

The previous prime is 21420331. The next prime is 21420403. The reversal of 21420397 is 79302412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20241001 + 1179396 = 4499^2 + 1086^2 .

It is a cyclic number.

It is not a de Polignac number, because 21420397 - 2¹¹ = 21418349 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21420097) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10710198 + 10710199.

It is an arithmetic number, because the mean of its divisors is an integer number (10710199).

Almost surely, 2^21420397 is an apocalyptic number.

It is an amenable number.

21420397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21420397 is an equidigital number, since it uses as much as digits as its factorization.

21420397 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 21420397 is about 4628.2174754434. The cubic root of 21420397 is about 277.7212887383.

The spelling of 21420397 in words is "twenty-one million, four hundred twenty thousand, three hundred ninety-seven".