21939391 has 2 divisors, whose sum is σ = 21939392. Its totient is φ = 21939390.

The previous prime is 21939383. The next prime is 21939419. The reversal of 21939391 is 19393912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21939391 - 2³ = 21939383 is a prime.

It is equal to p_1385677 and since 21939391 and 1385677 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21939391.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21939361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10969695 + 10969696.

It is an arithmetic number, because the mean of its divisors is an integer number (10969696).

Almost surely, 2^21939391 is an apocalyptic number.

21939391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21939391 is an equidigital number, since it uses as much as digits as its factorization.

21939391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13122, while the sum is 37.

The square root of 21939391 is about 4683.9503626747. The cubic root of 21939391 is about 279.9463800386.

The spelling of 21939391 in words is "twenty-one million, nine hundred thirty-nine thousand, three hundred ninety-one".