77

Number
$77$ (seventy-seven) is:
 * $7 \times 11$


 * The $26$th semiprime:
 * $77 = 7 \times 11$


 * The $7$th second pentagonal number after $2, 7, 15, 26, 40, 57$:
 * $77 = \dfrac {7 \left({3 \times 7 + 1}\right)} 2$


 * The $14$th generalized pentagonal number after $1, 2, 5, 7, 12, 15, 22, 26, 35, 40, 51, 57, 70$:
 * $77 = \dfrac {7 \left({3 \times 7 + 1}\right)} 2$


 * The $34$th integer $n$ such that $2^n$ contains no zero in its decimal representation:
 * $2^{77} = 151 \, 115 \, 727 \, 451 \, 828 \, 646 \, 838 \, 272$


 * The largest positive integer which cannot be expressed as the sum of positive integers whose reciprocals add up to $1$.


 * The $41$st positive integer after $2, 3, 4, 7, 8, \ldots, 50, 54, 55, 59, 60, 61, 65, 66, 67, 72$ which cannot be expressed as the sum of distinct pentagonal numbers.


 * The smallest (positive) integer which requires $5$ syllables to say it in the English language:
 * sev-en-ty-sev-en

Also see

 * Positive Integers Expressible by Sum of Integers whose Reciprocals Sum to 1