21783947 has 2 divisors, whose sum is σ = 21783948. Its totient is φ = 21783946.

The previous prime is 21783887. The next prime is 21783989. The reversal of 21783947 is 74938712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21783947 - 2¹⁰ = 21782923 is a prime.

It is not a weakly prime, because it can be changed into another prime (21783347) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10891973 + 10891974.

It is an arithmetic number, because the mean of its divisors is an integer number (10891974).

Almost surely, 2^21783947 is an apocalyptic number.

21783947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21783947 is an equidigital number, since it uses as much as digits as its factorization.

21783947 is an evil number, because the sum of its binary digits is even.

The product of its digits is 84672, while the sum is 41.

The square root of 21783947 is about 4667.3276079573. The cubic root of 21783947 is about 279.2836578439.

The spelling of 21783947 in words is "twenty-one million, seven hundred eighty-three thousand, nine hundred forty-seven".