Question 62
Triangular sequence. What is the $21^{\text{st}}$ term of the sequence
$$
1 ; 2+3 ; 4+5+6 ; 7+8+9+10 ; 11+12+13+14+15 ; \ldots ?
$$
$$
1 ; 2+3 ; 4+5+6 ; 7+8+9+10 ; 11+12+13+14+15 ; \ldots ?
$$
MathNet 2007-part-01 — 187 problems (EN–VI) Question 62
Math Olympiad Vault · MathNet 2007-part-01 — 187 problems (EN–VI)