The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A174797 Numbers n such that both semiprime(n) and semiprime(n+1) are even. 2

%I #8 Apr 20 2014 03:06:58

%S 1,4,21,87,120,141,142,168,188,320,363,387,434,464,496,539,593,675,

%T 721,794,810,995,1032,1105,1147,1166,1228,1356,1391,1477,1478,1498,

%U 1702,1771,1790,1797,1803,1818,1849,1850,1881,1967,2016,2039,2052,2065,2091

%N Numbers n such that both semiprime(n) and semiprime(n+1) are even.

%C Semiprime(n)/2 and semiprime(n+1)/2 are consecutive primes.

%H Vincenzo Librandi, <a href="/A174797/b174797.txt">Table of n, a(n) for n = 1..2000</a>

%F A001358(a(n)) = 2*A000040(A174798(n)).

%e a(1)=1 because both semiprime(1)=4 and semiprime(2)=6 are even

%e a(2)=4 because both semiprime(4)=10 and semiprime(5)=14 are even.

%t Flatten[Position[Partition[Select[Range[10000],PrimeOmega[#]==2&],2,1],_?(EvenQ[First[#]]&&EvenQ[Last[#]]&),{1},Heads->False]] (* _Harvey P. Dale_, Apr 19 2014 *)

%Y Cf. A000040, A001358, A174798.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Mar 29 2010

%E Edited and corrected by _Ray Chandler_, Apr 07 2010

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 18 20:35 EDT 2024. Contains 376002 sequences. (Running on oeis4.)