Perplexing puzzles

Here's the answers to the ones from June 30th

a) 5, 12, 19, 26, 33 , 40 -- 7xtable -2
b) 3, 9, 18, 30, 45 , 63 -- 3x triangle numbers
c) r, o, y, g, b, i -- colours of the rainbow

Here’s the next lot - they're getting harder ...

Give me the next 2 in each of these sequences:
a. 34, 29, 24, 19, __, __
b. 0.5, 2, 4.5, 8, __, __
c. o, t, t, f, __, __
Good luck. I will be giving the answers some time in the next month.
The second one is a little tricksy - if you want a clue, scroll down.


Never heard of triangle numbers?

Like square numbers make squares, triangle numbers make triangles. People like me think it's very cool - others (like most of the world) not so much.
Hopefully the pix below will make it clear.

Extra bonus points to anyone who can tell me what happens when you add two consecutive triangle numbers. So-oo cool.














Clue: If you don’t like decimals, try doubling.