OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
3 is a term because 3 = semiprime(2)/2 = 6/2 and 3 + 2 = 5 = semiprime(2+2)/2 = 10/2.
MAPLE
From R. J. Mathar, Apr 27 2010: (Start)
isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc:
A001358 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if isA001358(a) then return a; end if; end do: end if ; end proc:
A174956 := proc(p) for n from 1 do if A001358(n) = p then return n; elif A001358(n) > p then return 0 ; end if; end do: end proc:
A001359 := proc(n) option remember; if n = 1 then 3; else for a from procname(n-1)+2 by 2 do if isprime(a) and isprime(a+2) then return a; end if; end do: end if; end proc:
MATHEMATICA
(Select[Partition[Select[Range[6000], PrimeOmega[#]==2&], 3, 1], AllTrue[ {#[[1]]/2 , #[[3]]/2}, PrimeQ]&&#[[3]]-#[[1]]==4&]/2)[[All, 1]] (* Harvey P. Dale, Sep 24 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Apr 26 2010
EXTENSIONS
Corrected (541 replaced by 521, 1047 replaced by 1049, 1741 replaced by 1721) by R. J. Mathar, Apr 27 2010
STATUS
approved