21320987 has 2 divisors, whose sum is σ = 21320988. Its totient is φ = 21320986.

The previous prime is 21320969. The next prime is 21321019. The reversal of 21320987 is 78902312.

It is an a-pointer prime, because the next prime (21321019) can be obtained adding 21320987 to its sum of digits (32).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21320987 - 2¹² = 21316891 is a prime.

It is a Chen prime.

It is a plaindrome in base 13.

It is not a weakly prime, because it can be changed into another prime (21320947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10660493 + 10660494.

It is an arithmetic number, because the mean of its divisors is an integer number (10660494).

Almost surely, 2^21320987 is an apocalyptic number.

21320987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21320987 is an equidigital number, since it uses as much as digits as its factorization.

21320987 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 21320987 is about 4617.4654302983. The cubic root of 21320987 is about 277.2909964818.

The spelling of 21320987 in words is "twenty-one million, three hundred twenty thousand, nine hundred eighty-seven".