21261381 has 8 divisors (see below), whose sum is σ = 29263104. Its totient is φ = 13716960.

The previous prime is 21261377. The next prime is 21261403. The reversal of 21261381 is 18316212.

21261381 = 1533² + 1534² + ... + 1541².

21261381 is nontrivially palindromic in base 2.

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

It is not a de Polignac number, because 21261381 - 2² = 21261377 is a prime.

It is a super-3 number, since 3×21261381³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21261481) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 114216 + ... + 114401.

It is an arithmetic number, because the mean of its divisors is an integer number (3657888).

Almost surely, 2^21261381 is an apocalyptic number.

It is an amenable number.

21261381 is a deficient number, since it is larger than the sum of its proper divisors (8001723).

21261381 is a wasteful number, since it uses less digits than its factorization.

21261381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 228651.

The product of its digits is 576, while the sum is 24.

The square root of 21261381 is about 4611.0065061763. The cubic root of 21261381 is about 277.0323525228.

Adding to 21261381 its reverse (18316212), we get a palindrome (39577593).

The spelling of 21261381 in words is "twenty-one million, two hundred sixty-one thousand, three hundred eighty-one".