1595. the intervals of 2,7,26,101,400 are 5,19,75,299. The intervals of 5,19,75,299 are 14,56,224. 14,56,224 are 2^1x7, 2^3x7 and 2^5x7. Therefore the next interval of intervals will be 2^7x7= 896. So this means that the previous sequence will be 5,19,75,299,(299+896) or 5,19,75,299,1195. Therefore the next number in the original sequence is 400+1195 which equals 1595. 2,7,26,101,400,1595
For sequence 7,21,8,72,9 7,(7x3^1), 8, (8x3^2), 9, (9x3^3) so 7,21,8,72,9, 243