21691281 has 8 divisors (see below), whose sum is σ = 29329344. Its totient is φ = 14257040.

The previous prime is 21691279. The next prime is 21691283. The reversal of 21691281 is 18219612.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21691279) and next prime (21691283).

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 21691281 - 2¹ = 21691279 is a prime.

It is a super-2 number, since 2×21691281² = 941023342841922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21691283) 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, 50706 + ... + 51131.

It is an arithmetic number, because the mean of its divisors is an integer number (3666168).

Almost surely, 2^21691281 is an apocalyptic number.

It is an amenable number.

21691281 is a deficient number, since it is larger than the sum of its proper divisors (7638063).

21691281 is a wasteful number, since it uses less digits than its factorization.

21691281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 101911.

The product of its digits is 1728, while the sum is 30.

The square root of 21691281 is about 4657.3899342872. The cubic root of 21691281 is about 278.8870831975.

The spelling of 21691281 in words is "twenty-one million, six hundred ninety-one thousand, two hundred eighty-one".