21361391 has 2 divisors, whose sum is σ = 21361392. Its totient is φ = 21361390.

The previous prime is 21361303. The next prime is 21361397. The reversal of 21361391 is 19316312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21361391 - 2¹⁴ = 21345007 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21361391.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21361397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10680695 + 10680696.

It is an arithmetic number, because the mean of its divisors is an integer number (10680696).

Almost surely, 2^21361391 is an apocalyptic number.

21361391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21361391 is an equidigital number, since it uses as much as digits as its factorization.

21361391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 972, while the sum is 26.

The square root of 21361391 is about 4621.8384870093. The cubic root of 21361391 is about 277.4660445968.

The spelling of 21361391 in words is "twenty-one million, three hundred sixty-one thousand, three hundred ninety-one".