This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A118908 a(1) = 4; a(n) is greatest semiprime < a(n-1)^2. 5
 4, 15, 221, 48839, 2385247913, 5689407606470855563, 32369358912568429679140929317208046943, 1047775396410673232345014594095988998399127191704501568910205139392491645247 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Semiprime analogue of A059785 a(n+1)=prevprime(a(n)^2), with a(1) = 2. With that, of course, there's always a prime between n and 2n, so a(n) < 2^n. See also A055496 a(1) = 2; a(n) is smallest prime > 2*a(n-1). The obverse of this is A118909 a(1) = 4; a(n) is least semiprime > a(n-1)^2. LINKS EXAMPLE a(6) = 32369358912568429679140929317208046943 = 1816568472934912211 * 17818958874845686213 = 5689407606470855563^2 - 26 < a(5)^2. CROSSREFS Cf. A001358, A055496, A076656, A006992, A005384, A005385, A118908-A118913. Sequence in context: A197934 A137654 A195569 * A153060 A139244 A090115 Adjacent sequences:  A118905 A118906 A118907 * A118909 A118910 A118911 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, May 05 2006 STATUS approved

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 .