21208421397 has 4 divisors (see below), whose sum is σ = 28277895200. Its totient is φ = 14138947596.

The previous prime is 21208421393. The next prime is 21208421407. The reversal of 21208421397 is 79312480212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21208421397 - 2² = 21208421393 is a prime.

It is a super-3 number, since 3×21208421397³ (a number of 32 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21208421393) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3534736897 + ... + 3534736902.

It is an arithmetic number, because the mean of its divisors is an integer number (7069473800).

Almost surely, 2^21208421397 is an apocalyptic number.

It is an amenable number.

21208421397 is a deficient number, since it is larger than the sum of its proper divisors (7069473803).

21208421397 is an equidigital number, since it uses as much as digits as its factorization.

21208421397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7069473802.

The product of its (nonzero) digits is 48384, while the sum is 39.

The spelling of 21208421397 in words is "twenty-one billion, two hundred eight million, four hundred twenty-one thousand, three hundred ninety-seven".