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 A173231 a(n) is the n-th number m such that 6*m-1 is composite plus the n-th number k such that 6*k+1 is composite. 1
 10, 19, 22, 30, 35, 40, 44, 48, 51, 59, 63, 66, 70, 73, 80, 87, 90, 93, 95, 102, 104, 106, 110, 115, 119, 122, 126, 132, 134, 138, 142, 147, 153, 156, 161, 165, 168, 171, 174, 176, 178, 184, 186, 193, 195, 198, 202, 204, 210, 216, 221, 224, 227, 230, 234, 236 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A001477 = A002822 U A171696 U A067611 where A067611 = A121763 U A121765; A121763 = A046954 U A171696 and A121765 = A046953 U A171696. LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A046953(n) + A046954(n+1). EXAMPLE a(1) = 6 + 4 = 10; a(2) = 11 + 8 = 19; a(3) = 13 + 9 = 22. MAPLE A046953 := proc(n) if n = 1 then 6 ; else for a from procname(n-1)+1 do if not isprime(6*a-1) then return a; end if; end do: end if; end proc: A046954 := proc(n) if n = 1 then 0 ; else for a from procname(n-1)+1 do if not isprime(6*a+1) then return a; end if; end do: end if; end proc: A173231 := proc(n) A046953(n)+A046954(n+1) ; end proc: seq(A173231(n), n=1..120) ; # R. J. Mathar, May 02 2010 MATHEMATICA A046953:= Select[Range[250], !PrimeQ[6#-1] &]; A046954:= Select[Range[0, 250], !PrimeQ[6#+1] &]; Table[A046953[[n]] +A046954[[n+1]], {n, 1, 80}] PROG (MAGMA) A046953:=[n: n in [1..250] | not IsPrime(6*n-1)]; A046954:=[n: n in [0..250] | not IsPrime(6*n+1)]; [A046953[n] + A046954[n+1]: n in [1..80]]; // G. C. Greubel, Feb 21 2019 (Sage) A046953=[n for n in (1..250) if not is_prime(6*n-1)]; A046954=[n for n in (0..250) if not is_prime(6*n+1)]; [A046953[n] + A046954[n+1] for n in (0..80)] # G. C. Greubel, Feb 21 2019 (GAP) A046953:=Filtered([1..250], k-> not IsPrime(6*k-1));; A046954:=Filtered([0..250], n-> not IsPrime(6*n+1));; Print(List([1..80], j->A046953[j]+A046954[j+1])); # G. C. Greubel, Feb 21 2019 CROSSREFS Cf. A001477, A002822, A067611, A046953, A046954, A121763, A121765, A171696. Sequence in context: A061016 A038366 A210539 * A172055 A249648 A260263 Adjacent sequences:  A173228 A173229 A173230 * A173232 A173233 A173234 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Feb 13 2010, Feb 15 2010 EXTENSIONS Entries checked by R. J. Mathar, May 02 2010 STATUS approved

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Last modified September 22 19:36 EDT 2021. Contains 347608 sequences. (Running on oeis4.)