21667987 has 8 divisors (see below), whose sum is σ = 24141312. Its totient is φ = 19278600.

The previous prime is 21667973. The next prime is 21668011. The reversal of 21667987 is 78976612.

It is a happy number.

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

It is not a de Polignac number, because 21667987 - 2⁷ = 21667859 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21667187) 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, 20439 + ... + 21472.

It is an arithmetic number, because the mean of its divisors is an integer number (3017664).

Almost surely, 2^21667987 is an apocalyptic number.

21667987 is a deficient number, since it is larger than the sum of its proper divisors (2473325).

21667987 is a wasteful number, since it uses less digits than its factorization.

21667987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41969.

The product of its digits is 254016, while the sum is 46.

The square root of 21667987 is about 4654.8885056465. Note that the first 3 decimals coincide. The cubic root of 21667987 is about 278.7872163036.

It can be divided in two parts, 2166 and 7987, that added together give a triangular number (10153 = T₁₄₂).

The spelling of 21667987 in words is "twenty-one million, six hundred sixty-seven thousand, nine hundred eighty-seven".