login
This site is supported by donations to The OEIS Foundation.
Logo

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A102782 Repunit semiprimes. 5
111, 1111, 11111, 1111111, 11111111111, 11111111111111111, 11111111111111111111111111111111111111111111111, 11111111111111111111111111111111111111111111111111111111111 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

FORMULA

a(n) = A000042(A046413(n-1)). - Ray Chandler (rayjchandler(AT)sbcglobal.net), Sep 06 2005

EXAMPLE

a(2)=1111 because 1111=11*101, so 1111 is semiprime as well as a repunit number.

CROSSREFS

Cf. A046413 the repunit of length n has exactly 2 prime factors.

Sequence in context: A115816 A115877 A199979 * A137465 A101152 A075859

Adjacent sequences:  A102779 A102780 A102781 * A102783 A102784 A102785

KEYWORD

base,nonn

AUTHOR

Shyam Sunder Gupta (guptass(AT)rediffmail.com), Feb 11 2005

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified February 14 23:53 EST 2012. Contains 205689 sequences.