21173987 has 2 divisors, whose sum is σ = 21173988. Its totient is φ = 21173986.

The previous prime is 21173983. The next prime is 21174001. The reversal of 21173987 is 78937112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21173987 - 2² = 21173983 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21173987.

It is not a weakly prime, because it can be changed into another prime (21173983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586993 + 10586994.

It is an arithmetic number, because the mean of its divisors is an integer number (10586994).

Almost surely, 2^21173987 is an apocalyptic number.

21173987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21173987 is an equidigital number, since it uses as much as digits as its factorization.

21173987 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21168, while the sum is 38.

The square root of 21173987 is about 4601.5200749318. The cubic root of 21173987 is about 276.6522546968.

The spelling of 21173987 in words is "twenty-one million, one hundred seventy-three thousand, nine hundred eighty-seven".