21664471 has 2 divisors, whose sum is σ = 21664472. Its totient is φ = 21664470.

The previous prime is 21664457. The next prime is 21664483. The reversal of 21664471 is 17446612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21664471 - 2⁷ = 21664343 is a prime.

It is a super-3 number, since 3×21664471³ (a number of 23 digits) contains 333 as substring.

It is equal to p_1369309 and since 21664471 and 1369309 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21664771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832235 + 10832236.

It is an arithmetic number, because the mean of its divisors is an integer number (10832236).

Almost surely, 2^21664471 is an apocalyptic number.

21664471 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664471 is an equidigital number, since it uses as much as digits as its factorization.

21664471 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 31.

The square root of 21664471 is about 4654.5108228470. The cubic root of 21664471 is about 278.7721361629.

The spelling of 21664471 in words is "twenty-one million, six hundred sixty-four thousand, four hundred seventy-one".