21355987 has 2 divisors, whose sum is σ = 21355988. Its totient is φ = 21355986.

The previous prime is 21355969. The next prime is 21356003. The reversal of 21355987 is 78955312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21355987 - 2¹¹ = 21353939 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21355967) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10677993 + 10677994.

It is an arithmetic number, because the mean of its divisors is an integer number (10677994).

Almost surely, 2^21355987 is an apocalyptic number.

21355987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21355987 is an equidigital number, since it uses as much as digits as its factorization.

21355987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 75600, while the sum is 40.

The square root of 21355987 is about 4621.2538341883. The cubic root of 21355987 is about 277.4426448571.

The spelling of 21355987 in words is "twenty-one million, three hundred fifty-five thousand, nine hundred eighty-seven".