21515221081 has 8 divisors (see below), whose sum is σ = 21540998528. Its totient is φ = 21489462000.

The previous prime is 21515221069. The next prime is 21515221087. The reversal of 21515221081 is 18012251512.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a 3-Lehmer number, since φ(21515221081) divides (21515221081-1)³.

It is a cyclic number.

It is a Carmichael number.

It is not a de Polignac number, because 21515221081 - 2⁷ = 21515220953 is a prime.

It is a super-2 number, since 2×21515221081² (a number of 21 digits) contains 22 as substring.

It is a deceptive number, since it divides R_21515221080.

It is not an unprimeable number, because it can be changed into a prime (21515221087) by changing a digit.

It is a Zeisel number, with parameters (1, 1530).

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4684096 + ... + 4688686.

It is an arithmetic number, because the mean of its divisors is an integer number (2692624816).

It is a Poulet number, since it divides 2^21515221080-1.

Almost surely, 2^21515221081 is an apocalyptic number.

It is an amenable number.

21515221081 is a deficient number, since it is larger than the sum of its proper divisors (25777447).

21515221081 is a wasteful number, since it uses less digits than its factorization.

21515221081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9183.

The product of its (nonzero) digits is 1600, while the sum is 28.

Adding to 21515221081 its reverse (18012251512), we get a palindrome (39527472593).

The spelling of 21515221081 in words is "twenty-one billion, five hundred fifteen million, two hundred twenty-one thousand, eighty-one".