21787691 has 2 divisors, whose sum is σ = 21787692. Its totient is φ = 21787690.

The previous prime is 21787681. The next prime is 21787723. The reversal of 21787691 is 19678712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21787691 - 2¹⁴ = 21771307 is a prime.

It is a super-2 number, since 2×21787691² = 949406958222962, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21787651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10893845 + 10893846.

It is an arithmetic number, because the mean of its divisors is an integer number (10893846).

Almost surely, 2^21787691 is an apocalyptic number.

21787691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21787691 is an equidigital number, since it uses as much as digits as its factorization.

21787691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 42336, while the sum is 41.

The square root of 21787691 is about 4667.7286767763. The cubic root of 21787691 is about 279.2996570583.

The spelling of 21787691 in words is "twenty-one million, seven hundred eighty-seven thousand, six hundred ninety-one".