About the Number 991 (nine hundred ninety-one)

@MathBabbler received the following tweet from @MAAnow on 2010.03.01.

   Today's Number: 991 http://cot.ag/9bnoi7
   MathBabbler Number Analyst (MBNA) output:
   =========================================
   991 is a natural, whole, integer
   991 is odd
   991 proper divisors are: 1,
   991 is deficient (sum of divisors is 1)
   991 is unhappy
   991 is not a Harshad number
   991 is prime
   ...Sexy prime with 997
	...OEIS:002145 (4n+3; n=247)
   ...Super
   991 is a lucky number
   991 is the sum of 7 consecutive primes
   991 = 127 + 131 + 137 + 139 + 149 + 151 + 157
   991 in octal is 01737
   991 in hexadecimal is 0x3df
   991 in binary is 1111011111 (is odious)
   991 nearest square numbers: -30...33 (961...1024 [32])
   sqrt(991) = 31.4802
   ln(991) = 6.89871
   log(991) = 2.99607
   991 reciprocal is .00100908173562058526740665993945
   991! is 4.1718e+2540
   991 is 315.445 Pi years
   991 is 49 score and 11 years
   991 written as a Roman numeral is CMXCI
   991 = 496^2 - 495^2 and 496 + 495 = 991

The MAA's NumberADay indicated that 991 is the "largest three-digit permutable prime. In other words, 991, 919, and 199 are all primes."


Creator: Gerald Thurman [gthurman@gmail.com]
Created: 01 March 2010

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