61721781 has 32 divisors (see below), whose sum is σ = 95644800. Its totient is φ = 34990080.

The previous prime is 61721761. The next prime is 61721783. The reversal of 61721781 is 18712716.

It is not a de Polignac number, because 61721781 - 2⁵ = 61721749 is a prime.

It is a super-2 number, since 2×61721781² = 7619156499623922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61721783) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 150705 + ... + 151113.

It is an arithmetic number, because the mean of its divisors is an integer number (2988900).

Almost surely, 2^61721781 is an apocalyptic number.

It is an amenable number.

61721781 is a deficient number, since it is larger than the sum of its proper divisors (33923019).

61721781 is a wasteful number, since it uses less digits than its factorization.

61721781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 709.

The product of its digits is 4704, while the sum is 33.

The square root of 61721781 is about 7856.3210855973. The cubic root of 61721781 is about 395.1962513543.

The spelling of 61721781 in words is "sixty-one million, seven hundred twenty-one thousand, seven hundred eighty-one".