15 = 3 x 5

15 = 2^0 + 2^1 + 2^2 + 2^3 = 2^4 -1

15 is a triangular number.

15 = 3 + 5 + 7, i.e. the sum of 3 consecutive prime numbers.

15 is the fourth cake number.

15 is a member of the primitive, Pythagorean triple (8, 15, 17).

15 is the fifth Toothpick number.

15 is the smallest emirpimes.

15 is a lucky number.

15 is the fourth Bell number.

15 is the number of distinct rhyme schemes for a poem of 4 lines.

The 15 rhyme schemes are:

aaaa

aaab

aaba

aabb

aabc

abaa

abab

abac

abba

abbb

abbc

abca

abcb

abcc

abcd

15 is the number of moves required to solve the frogs and toads game with 3 of each.

The moves are:

FFF_TTT

FFFT_TT - Slide T3

FF_TFTT - Jump F3

F_FTFTT - Slide F2

FTF_FTT - Jump T3

FTFTF_T - Jump T2

FTFTFT_ - Slide T1

FTFT_TF - Jump F3

FT_TFTF - Jump F2

_TFTFTF - Jump F1

T_FTFTF - Slide T3

TTF_FTF - Jump T2

TTFTF_F - Jump T1

TTFT_FF - Slide F2

TT_TFFF - Jump F1

TTT_FFF - Slide T3

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