Reschedule Times Table for 5s plus N^4

By default, DelayedJob reschedules erroring jobs in 5 seconds + N ** 4, where N is the number of attempts.

These figures assume the job always runs on schedule (at run_at time) and runs in 0 seconds.

Number of attempts (N)	Delay	Cumulative delay
1	6s	6s
2	21s	27s
3	86s	113s
4	261s	374s
5	630s	1,004s
6	1,301s	2,305s
7	2,406s	4,711s
8	4,101s	8,812s
9	6,566s	15,378s
10	10,005s	25,383s
11	14,646s	40,029s
12	20,741s	60,770s
13	28,566s	89,336s
14	38,421s	127,757s
15	50,630s	178,387s
16	65,541s	243,928s
17	83,526s	327,454s
18	104,981s	432,435s
19	130,326s	562,761s
20	160,005s	722,766s
21	194,486s	917,252s
22	234,261s	1,151,513s
23	279,846s	1,431,359s
24	331,781s	1,763,140s
25	390,630s	2,153,770s