21017951 has 2 divisors, whose sum is σ = 21017952. Its totient is φ = 21017950.

The previous prime is 21017897. The next prime is 21017981. The reversal of 21017951 is 15971012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21017951 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21017951.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21017981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10508975 + 10508976.

It is an arithmetic number, because the mean of its divisors is an integer number (10508976).

Almost surely, 2^21017951 is an apocalyptic number.

21017951 is a deficient number, since it is larger than the sum of its proper divisors (1).

21017951 is an equidigital number, since it uses as much as digits as its factorization.

21017951 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 630, while the sum is 26.

The square root of 21017951 is about 4584.5338912478. The cubic root of 21017951 is about 275.9710070714.

Adding to 21017951 its reverse (15971012), we get a palindrome (36988963).

The spelling of 21017951 in words is "twenty-one million, seventeen thousand, nine hundred fifty-one".