21393481 has 2 divisors, whose sum is σ = 21393482. Its totient is φ = 21393480.

The previous prime is 21393467. The next prime is 21393521. The reversal of 21393481 is 18439312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13995081 + 7398400 = 3741^2 + 2720^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21393481 is a prime.

It is a super-2 number, since 2×21393481² = 915362058594722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21393461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10696740 + 10696741.

It is an arithmetic number, because the mean of its divisors is an integer number (10696741).

Almost surely, 2^21393481 is an apocalyptic number.

It is an amenable number.

21393481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21393481 is an equidigital number, since it uses as much as digits as its factorization.

21393481 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 31.

The square root of 21393481 is about 4625.3087464514. The cubic root of 21393481 is about 277.6049155546.

The spelling of 21393481 in words is "twenty-one million, three hundred ninety-three thousand, four hundred eighty-one".