21512881 has 8 divisors (see below), whose sum is σ = 23486120. Its totient is φ = 19585152.

The previous prime is 21512861. The next prime is 21512893. The reversal of 21512881 is 18821512.

It can be written as a sum of positive squares in 4 ways, for example, as 5640625 + 15872256 = 2375^2 + 3984^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21512881 - 2¹¹ = 21510833 is a prime.

It is a super-2 number, since 2×21512881² = 925608097840322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21512801) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10386 + ... + 12283.

It is an arithmetic number, because the mean of its divisors is an integer number (2935765).

Almost surely, 2^21512881 is an apocalyptic number.

It is an amenable number.

21512881 is a deficient number, since it is larger than the sum of its proper divisors (1973239).

21512881 is a wasteful number, since it uses less digits than its factorization.

21512881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22755.

The product of its digits is 1280, while the sum is 28.

The square root of 21512881 is about 4638.1980337196. The cubic root of 21512881 is about 278.1204083070.

The spelling of 21512881 in words is "twenty-one million, five hundred twelve thousand, eight hundred eighty-one".