20139991 has 2 divisors, whose sum is σ = 20139992. Its totient is φ = 20139990.

The previous prime is 20139983. The next prime is 20139997. The reversal of 20139991 is 19993102.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20139991 - 2³ = 20139983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20139997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10069995 + 10069996.

It is an arithmetic number, because the mean of its divisors is an integer number (10069996).

Almost surely, 2^20139991 is an apocalyptic number.

20139991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20139991 is an equidigital number, since it uses as much as digits as its factorization.

20139991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 20139991 is about 4487.7601317361. The cubic root of 20139991 is about 272.0736131136.

The spelling of 20139991 in words is "twenty million, one hundred thirty-nine thousand, nine hundred ninety-one".