21881647 has 2 divisors, whose sum is σ = 21881648. Its totient is φ = 21881646.

The previous prime is 21881627. The next prime is 21881653. The reversal of 21881647 is 74618812.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21881647 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21881627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10940823 + 10940824.

It is an arithmetic number, because the mean of its divisors is an integer number (10940824).

Almost surely, 2^21881647 is an apocalyptic number.

21881647 is a deficient number, since it is larger than the sum of its proper divisors (1).

21881647 is an equidigital number, since it uses as much as digits as its factorization.

21881647 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 21504, while the sum is 37.

The square root of 21881647 is about 4677.7822736848. The cubic root of 21881647 is about 279.7005599865.

The spelling of 21881647 in words is "twenty-one million, eight hundred eighty-one thousand, six hundred forty-seven".