20921947 has 2 divisors, whose sum is σ = 20921948. Its totient is φ = 20921946.

The previous prime is 20921911. The next prime is 20921959. The reversal of 20921947 is 74912902.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20921947 - 2⁷ = 20921819 is a prime.

It is not a weakly prime, because it can be changed into another prime (20921987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10460973 + 10460974.

It is an arithmetic number, because the mean of its divisors is an integer number (10460974).

Almost surely, 2^20921947 is an apocalyptic number.

20921947 is a deficient number, since it is larger than the sum of its proper divisors (1).

20921947 is an equidigital number, since it uses as much as digits as its factorization.

20921947 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 34.

The square root of 20921947 is about 4574.0514863740. The cubic root of 20921947 is about 275.5501800882.

The spelling of 20921947 in words is "twenty million, nine hundred twenty-one thousand, nine hundred forty-seven".