31 is a Prime Number
Sexy Prime (Primes p such that p + 6 is also prime)
Prime of the form 2x^2 + 13y^2.
31 = 25 − 1, Mersenne number: 2^p - 1, p Prime, 231 - 1 = 2147483647
31 = 50 + 51 + 52 = 20 + 21 + 22 + 23 + 24
31 = 12345 + 6 + 7 + 8 + 9
31 = 98 − 76 − 5 − 4 − 3 + 21
31 = 0^6 + 1^7 + 2^9 − 3^8 + 4^1 + 5^5 + 6^2 + 7^4 + 8^3 + 9^0
31 = (1 + 1 + 1) × (11 − 1) + 1
= 22 + (2 + 2/2)2
= 3 + 33 + 3/3
= 4 × (4 + 4) − 4/4 = = 4!+ (4!+4)÷4.
= 5 × 5 + 5 + 5/5
= 6 × 6 − 6 + 6/6
= 7 × 7 − 7 − 77/7
= 8 + 8 + 8 + 8 − 8/8
= 9 + (99 + 99)/9
31 = 1 + 2 + 2^2 + 2^3 + 2^4 = 1 + 5 + 5^2
1031 - 1 = 3 * 3 * 2791 * 6943319 * 57336415063790604359
31 is the only known prime to be 31 = sigma(16) = sigma(25) .
Number k such that k^2+k+7 is a palindrome
Number k such that 9^k + 8^(k-1) is prime.
Number k such that (13^k - 3^k)/10 is prime.
Difference of two positive 5th powers.
Maximal number of regions obtained by joining 6 points around a circle by straight lines
Björner-Welker sequence: 2^n*(n^2 + n + 2) - 1. n = 2
Emirp , 13 is also Prime
31 cannot be written as a sum of 3 squares. (Integers that are not a sum of three squares)
Factors: 1, 31
Representations, Binary to Hexadecimal:
11111_2
1011_3
133_4
111_5
51_6
43_7
37_8
34_9
29_11
27_12
25_13
23_14
21_15
1f_16:
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Undergraduate Texts in Mathematics
Graduate Studies in Mathematics
