21516947 has 2 divisors, whose sum is σ = 21516948. Its totient is φ = 21516946.

The previous prime is 21516919. The next prime is 21516959. The reversal of 21516947 is 74961512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21516947 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21518947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758473 + 10758474.

It is an arithmetic number, because the mean of its divisors is an integer number (10758474).

Almost surely, 2^21516947 is an apocalyptic number.

21516947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21516947 is an equidigital number, since it uses as much as digits as its factorization.

21516947 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 35.

The square root of 21516947 is about 4638.6363297849. The cubic root of 21516947 is about 278.1379290711.

The spelling of 21516947 in words is "twenty-one million, five hundred sixteen thousand, nine hundred forty-seven".