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

Author

Reinhard Zumkeller, Mar 23 2014

Keywords

• nonn
• base

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