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

1,4

Links

Table of n, a(n) for n=1..57.

Example

.   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].

Prog

(Haskell)
import Data.List (group)
a239639 n = a239639_list !! (n-1)
a239639_list = map length $ group a239634_list

Crossrefs

Cf. A001358.

Sequence in context: A091828 A305972 A121845 * A099816 A237273 A272025

Adjacent sequences: A239636 A239637 A239638 * A239640 A239641 A239642

Keyword

nonn,base

Author

Reinhard Zumkeller, Mar 23 2014

Status

approved