21517819 has 2 divisors, whose sum is σ = 21517820. Its totient is φ = 21517818.

The previous prime is 21517781. The next prime is 21517843. The reversal of 21517819 is 91871512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21517819 - 2¹⁷ = 21386747 is a prime.

It is a super-2 number, since 2×21517819² = 926033069033522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21517849) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758909 + 10758910.

It is an arithmetic number, because the mean of its divisors is an integer number (10758910).

Almost surely, 2^21517819 is an apocalyptic number.

21517819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21517819 is an equidigital number, since it uses as much as digits as its factorization.

21517819 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5040, while the sum is 34.

The square root of 21517819 is about 4638.7303219739. The cubic root of 21517819 is about 278.1416863111.

The spelling of 21517819 in words is "twenty-one million, five hundred seventeen thousand, eight hundred nineteen".