A239639 Lengths of runs of the initial digits of semiprimes in decimal representation, cf. A239634.
1, 1, 1, 3, 4, 5, 2, 4, 3, 2, 4, 4, 28, 32, 32, 27, 33, 26, 30, 28, 29, 278, 264, 264, 260, 257, 245, 262, 252, 244, 2456, 2380, 2329, 2320, 2254, 2325, 2231, 2244, 2214, 21852, 21400, 20923, 20773, 20548, 20528, 20258, 20156, 20219, 197249, 193162, 190540, 188288, 187308, 185657, 184788, 183856, 183441
Offset: 1
Examples
. n | a(n) | runs in A001358 having a common initial digit . ----+------+------------------------------------------------------- . 1 | 1 | [4] . 2 | 1 | [6] . 3 | 1 | [9] . 4 | 3 | [10, 14, 15] . 5 | 4 | [21, 22, 25, 26] . 6 | 5 | [33, 34, 35, 38, 39] . 7 | 2 | [46, 49] . 8 | 4 | [51, 55, 57, 58] . 9 | 3 | [62, 65, 69] . 10 | 2 | [74, 77] . 11 | 4 | [82, 85, 86, 87] . 12 | 4 | [91, 93, 94, 95] . 13 | 28 | [106,111,115,118,119,121,122,123,129,133,134,141, . | | 142,143,145,146,155,158,159,161,166,169,177,178, . | | 183,185,187,194,201] . 14 | 32 | [201,202,203,205,206,209,213,214,215,217,218,219, . | | 221,226,235,237,247,249,253,254,259,262,265,267, . | | 274,278,287,289,291,295,298,299] . 15 | 32 | [301,302,303,305,309,314,319,321,323,326,327,329, . | | 334,335,339,341,346,355,358,361,362,365,371,377, . | | 381,382,386,391,393,394,395,398] . 16 | 27 | [403,407,411,413,415,417,422,427,437,445,446,447, . | | 451,453,454,458,466,469,471,473,478,481,482,485, . | | 489,493,497].
Crossrefs
Cf. A001358.
Programs
-
Haskell
import Data.List (group) a239639 n = a239639_list !! (n-1) a239639_list = map length $ group a239634_list