21111947 has 4 divisors (see below), whose sum is σ = 21246576. Its totient is φ = 20977320.

The previous prime is 21111931. The next prime is 21111991. The reversal of 21111947 is 74911112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21111947 - 2⁴ = 21111931 is a prime.

It is a super-2 number, since 2×21111947² = 891428612261618, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21111247) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 67079 + ... + 67392.

It is an arithmetic number, because the mean of its divisors is an integer number (5311644).

Almost surely, 2^21111947 is an apocalyptic number.

21111947 is a deficient number, since it is larger than the sum of its proper divisors (134629).

21111947 is a wasteful number, since it uses less digits than its factorization.

21111947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 134628.

The product of its digits is 504, while the sum is 26.

The square root of 21111947 is about 4594.7738790935. The cubic root of 21111947 is about 276.3817923868.

The spelling of 21111947 in words is "twenty-one million, one hundred eleven thousand, nine hundred forty-seven".