A067278 a(n) = letters(n) + a(n-1); a(0) = 0.
0, 3, 6, 11, 15, 19, 22, 27, 32, 36, 39, 45, 51, 59, 67, 74, 81, 90, 98, 106, 112, 121, 130, 141, 151, 161, 170, 181, 192, 202, 208, 217, 226, 237, 247, 257, 266, 277, 288, 298, 303, 311, 319, 329, 338, 347, 355, 365, 375, 384, 389, 397, 405, 415, 424, 433, 441
Offset: 0
Examples
0 + one = 3, 3 + two = 6, 6 + three = 11, 11 + four = 15, 15 + five = 19, ....
Formula
a(n) = A005589(n) + a(n-1). - Michael S. Branicky, Mar 03 2025