21606751 has 2 divisors, whose sum is σ = 21606752. Its totient is φ = 21606750.

The previous prime is 21606733. The next prime is 21606757. The reversal of 21606751 is 15760612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21606751 - 2⁵ = 21606719 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21606757) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10803375 + 10803376.

It is an arithmetic number, because the mean of its divisors is an integer number (10803376).

Almost surely, 2^21606751 is an apocalyptic number.

21606751 is a deficient number, since it is larger than the sum of its proper divisors (1).

21606751 is an equidigital number, since it uses as much as digits as its factorization.

21606751 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21606751 is about 4648.3062506681. The cubic root of 21606751 is about 278.5243412225.

It can be divided in two parts, 2160 and 6751, that added together give a triangular number (8911 = T₁₃₃).

The spelling of 21606751 in words is "twenty-one million, six hundred six thousand, seven hundred fifty-one".