21212397 has 6 divisors (see below), whose sum is σ = 30640142. Its totient is φ = 14141592.

The previous prime is 21212353. The next prime is 21212423. The reversal of 21212397 is 79321212.

It can be written as a sum of positive squares in only one way, i.e., 10850436 + 10361961 = 3294^2 + 3219^2 .

It is not a de Polignac number, because 21212397 - 2¹⁰ = 21211373 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21212397.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212197) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1178458 + ... + 1178475.

Almost surely, 2^21212397 is an apocalyptic number.

It is an amenable number.

21212397 is a deficient number, since it is larger than the sum of its proper divisors (9427745).

21212397 is a wasteful number, since it uses less digits than its factorization.

21212397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2356939 (or 2356936 counting only the distinct ones).

The product of its digits is 1512, while the sum is 27.

The square root of 21212397 is about 4605.6918047129. The cubic root of 21212397 is about 276.8194377311.

It can be divided in two parts, 21212 and 397, that added together give a square (21609 = 147²).

The spelling of 21212397 in words is "twenty-one million, two hundred twelve thousand, three hundred ninety-seven".