21317887 has 2 divisors, whose sum is σ = 21317888. Its totient is φ = 21317886.

The previous prime is 21317873. The next prime is 21317897. The reversal of 21317887 is 78871312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21317887 - 2⁷ = 21317759 is a prime.

It is a super-2 number, since 2×21317887² = 908904612289538, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21317897) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10658943 + 10658944.

It is an arithmetic number, because the mean of its divisors is an integer number (10658944).

Almost surely, 2^21317887 is an apocalyptic number.

21317887 is a deficient number, since it is larger than the sum of its proper divisors (1).

21317887 is an equidigital number, since it uses as much as digits as its factorization.

21317887 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18816, while the sum is 37.

The square root of 21317887 is about 4617.1297361023. The cubic root of 21317887 is about 277.2775567701.

The spelling of 21317887 in words is "twenty-one million, three hundred seventeen thousand, eight hundred eighty-seven".