21518947 has 2 divisors, whose sum is σ = 21518948. Its totient is φ = 21518946.

The previous prime is 21518933. The next prime is 21518969. The reversal of 21518947 is 74981512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21518947 - 2²³ = 13130339 is a prime.

It is not a weakly prime, because it can be changed into another prime (21518047) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10759473 + 10759474.

It is an arithmetic number, because the mean of its divisors is an integer number (10759474).

Almost surely, 2^21518947 is an apocalyptic number.

21518947 is a deficient number, since it is larger than the sum of its proper divisors (1).

21518947 is an equidigital number, since it uses as much as digits as its factorization.

21518947 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20160, while the sum is 37.

The square root of 21518947 is about 4638.8519053749. The cubic root of 21518947 is about 278.1465464434.

The spelling of 21518947 in words is "twenty-one million, five hundred eighteen thousand, nine hundred forty-seven".