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A088648 a(1) = 1, then the smallest odd number not occurring earlier such that the concatenation a(r), a(s) is composite for all s > r. 0
1, 5, 11, 15, 19, 25, 35, 45, 55, 65, 75, 85, 95, 105, 115, 125, 135, 145, 155, 165, 175, 185, 195, 205, 215, 225, 235, 245, 255, 265, 275, 285, 295, 305, 315, 325, 335, 345, 355, 365, 375, 385, 395, 405, 415, 425, 435, 445, 455, 465, 475, 485, 495, 505, 515 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The sequence is infinite with trivial terms of the form 10k+5. Subsidiary sequence: sequence of nontrivial terms. Conjecture: the subsidiary sequence is infinite.

LINKS

Table of n, a(n) for n=0..54.

EXAMPLE

a(5) = 19 as 119, 519,1119,1519, etc. are all composite.

CROSSREFS

Cf. A088647.

Sequence in context: A314013 A314014 A314015 * A314016 A314017 A314018

Adjacent sequences:  A088645 A088646 A088647 * A088649 A088650 A088651

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Oct 29 2003

EXTENSIONS

More terms from David Wasserman, Aug 17 2005

STATUS

approved

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Last modified August 2 08:40 EDT 2021. Contains 346422 sequences. (Running on oeis4.)