20649991 has 2 divisors, whose sum is σ = 20649992. Its totient is φ = 20649990.

The previous prime is 20649983. The next prime is 20649997. The reversal of 20649991 is 19994602.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20649991 - 2³ = 20649983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20649997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10324995 + 10324996.

It is an arithmetic number, because the mean of its divisors is an integer number (10324996).

Almost surely, 2^20649991 is an apocalyptic number.

20649991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20649991 is an equidigital number, since it uses as much as digits as its factorization.

20649991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 34992, while the sum is 40.

The square root of 20649991 is about 4544.2261167332. The cubic root of 20649991 is about 274.3510471979.

Subtracting from 20649991 its sum of digits (40), we obtain a triangular number (20649951 = T₆₄₂₆).

The spelling of 20649991 in words is "twenty million, six hundred forty-nine thousand, nine hundred ninety-one".