21677991 has 4 divisors (see below), whose sum is σ = 28903992. Its totient is φ = 14451992.

The previous prime is 21677989. The next prime is 21678001. The reversal of 21677991 is 19977612.

It is a happy number.

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 21677991 - 2¹ = 21677989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21677911) 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, 3612996 + ... + 3613001.

It is an arithmetic number, because the mean of its divisors is an integer number (7225998).

Almost surely, 2^21677991 is an apocalyptic number.

21677991 is a deficient number, since it is larger than the sum of its proper divisors (7226001).

21677991 is an equidigital number, since it uses as much as digits as its factorization.

21677991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7226000.

The product of its digits is 47628, while the sum is 42.

The square root of 21677991 is about 4655.9629508835. The cubic root of 21677991 is about 278.8301145849.

The spelling of 21677991 in words is "twenty-one million, six hundred seventy-seven thousand, nine hundred ninety-one".