21688761 has 16 divisors (see below), whose sum is σ = 29723904. Its totient is φ = 14060544.

The previous prime is 21688759. The next prime is 21688783. The reversal of 21688761 is 16788612.

It is not a de Polignac number, because 21688761 - 2¹ = 21688759 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21688721) 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, 26815 + ... + 27611.

It is an arithmetic number, because the mean of its divisors is an integer number (1857744).

Almost surely, 2^21688761 is an apocalyptic number.

It is an amenable number.

21688761 is a deficient number, since it is larger than the sum of its proper divisors (8035143).

21688761 is a wasteful number, since it uses less digits than its factorization.

21688761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1040.

The product of its digits is 32256, while the sum is 39.

The square root of 21688761 is about 4657.1193886350. The cubic root of 21688761 is about 278.8762828108.

The spelling of 21688761 in words is "twenty-one million, six hundred eighty-eight thousand, seven hundred sixty-one".