21151691 has 8 divisors (see below), whose sum is σ = 23112768. Its totient is φ = 19197000.

The previous prime is 21151687. The next prime is 21151721. The reversal of 21151691 is 19615112.

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 21151691 - 2² = 21151687 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21151691.

It is not an unprimeable number, because it can be changed into a prime (21151661) 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, 7736 + ... + 10106.

It is an arithmetic number, because the mean of its divisors is an integer number (2889096).

Almost surely, 2^21151691 is an apocalyptic number.

21151691 is a deficient number, since it is larger than the sum of its proper divisors (1961077).

21151691 is a wasteful number, since it uses less digits than its factorization.

21151691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3193.

The product of its digits is 540, while the sum is 26.

The square root of 21151691 is about 4599.0967591474. The cubic root of 21151691 is about 276.5551165595. Note that the first 3 decimals are identical.

The spelling of 21151691 in words is "twenty-one million, one hundred fifty-one thousand, six hundred ninety-one".