21503961 has 20 divisors (see below), whose sum is σ = 32279412. Its totient is φ = 14266368.

The previous prime is 21503947. The next prime is 21503969. The reversal of 21503961 is 16930512.

It can be written as a sum of positive squares in 2 ways, for example, as 20985561 + 518400 = 4581^2 + 720^2 .

It is not a de Polignac number, because 21503961 - 2¹¹ = 21501913 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21503969) by changing a digit.

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 19 ways as a sum of consecutive naturals, for example, 20301 + ... + 21333.

Almost surely, 2^21503961 is an apocalyptic number.

It is an amenable number.

21503961 is a deficient number, since it is larger than the sum of its proper divisors (10775451).

21503961 is a wasteful number, since it uses less digits than its factorization.

21503961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1302 (or 1293 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 21503961 is about 4637.2363536917. The cubic root of 21503961 is about 278.0819634794.

The spelling of 21503961 in words is "twenty-one million, five hundred three thousand, nine hundred sixty-one".