21518297407 has 4 divisors (see below), whose sum is σ = 21518596840. Its totient is φ = 21517997976.

The previous prime is 21518297371. The next prime is 21518297441. The reversal of 21518297407 is 70479281512.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a 3-Lehmer number, since φ(21518297407) divides (21518297407-1)³.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21518297407 is a prime.

It is a super-2 number, since 2×21518297407² (a number of 21 digits) contains 22 as substring.

It is a deceptive number, since it divides R_21518297406.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21518297707) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 29944 + ... + 209602.

It is an arithmetic number, because the mean of its divisors is an integer number (5379649210).

Almost surely, 2^21518297407 is an apocalyptic number.

21518297407 is the 119773-rd pentagonal number.

21518297407 is a deficient number, since it is larger than the sum of its proper divisors (299433).

21518297407 is a wasteful number, since it uses less digits than its factorization.

21518297407 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 299432.

The product of its (nonzero) digits is 282240, while the sum is 46.

The spelling of 21518297407 in words is "twenty-one billion, five hundred eighteen million, two hundred ninety-seven thousand, four hundred seven".