21371781 has 16 divisors (see below), whose sum is σ = 29082240. Its totient is φ = 13957440.

The previous prime is 21371767. The next prime is 21371797. The reversal of 21371781 is 18717312.

It is not a de Polignac number, because 21371781 - 2⁶ = 21371717 is a prime.

It is a super-2 number, since 2×21371781² = 913506046223922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21371281) 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 15 ways as a sum of consecutive naturals, for example, 57111 + ... + 57483.

It is an arithmetic number, because the mean of its divisors is an integer number (1817640).

Almost surely, 2^21371781 is an apocalyptic number.

It is an amenable number.

21371781 is a deficient number, since it is larger than the sum of its proper divisors (7710459).

21371781 is a wasteful number, since it uses less digits than its factorization.

21371781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 716.

The product of its digits is 2352, while the sum is 30.

The square root of 21371781 is about 4622.9623619493. The cubic root of 21371781 is about 277.5110230180.

The spelling of 21371781 in words is "twenty-one million, three hundred seventy-one thousand, seven hundred eighty-one".