21501381 has 16 divisors (see below), whose sum is σ = 31362048. Its totient is φ = 12994800.

The previous prime is 21501377. The next prime is 21501401. The reversal of 21501381 is 18310512.

It is not a de Polignac number, because 21501381 - 2² = 21501377 is a prime.

It is a super-2 number, since 2×21501381² = 924618769814322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21501371) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15540 + ... + 16866.

It is an arithmetic number, because the mean of its divisors is an integer number (1960128).

Almost surely, 2^21501381 is an apocalyptic number.

It is an amenable number.

21501381 is a deficient number, since it is larger than the sum of its proper divisors (9860667).

21501381 is a wasteful number, since it uses less digits than its factorization.

21501381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1832.

The product of its (nonzero) digits is 240, while the sum is 21.

The square root of 21501381 is about 4636.9581624164. The cubic root of 21501381 is about 278.0708418050.

Adding to 21501381 its reverse (18310512), we get a palindrome (39811893).

The spelling of 21501381 in words is "twenty-one million, five hundred one thousand, three hundred eighty-one".