21131505 has 12 divisors (see below), whose sum is σ = 36628020. Its totient is φ = 11270112.

The previous prime is 21131489. The next prime is 21131507. The reversal of 21131505 is 50513112.

It can be written as a sum of positive squares in 2 ways, for example, as 10556001 + 10575504 = 3249^2 + 3252^2 .

It is not a de Polignac number, because 21131505 - 2⁴ = 21131489 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21131507) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 234750 + ... + 234839.

It is an arithmetic number, because the mean of its divisors is an integer number (3052335).

Almost surely, 2^21131505 is an apocalyptic number.

It is an amenable number.

21131505 is a deficient number, since it is larger than the sum of its proper divisors (15496515).

21131505 is a wasteful number, since it uses less digits than its factorization.

21131505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 469600 (or 469597 counting only the distinct ones).

The product of its (nonzero) digits is 150, while the sum is 18.

The square root of 21131505 is about 4596.9016739539. The cubic root of 21131505 is about 276.4671122731.

Adding to 21131505 its reverse (50513112), we get a palindrome (71644617).

The spelling of 21131505 in words is "twenty-one million, one hundred thirty-one thousand, five hundred five".