This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A121765 #19 Dec 23 2024 13:43:43 %S A121765 6,11,13,16,21,26,27,35,37,46,51,55,56,61,62,63,66,68,73,76,81,83,90, %T A121765 91,96,101,102,105,112,115,118,121,122,123,125,126,128,131,142,146, %U A121765 151,153,156,161,165,166,168,173,178,181,186,187,188,195,200,202,206,208,216 %N A121765 Numbers n such that 6*n-1 is composite while 6*n+1 is prime. %C A121765 Entries in A046953 which are not in A060461 or equivalently, entries in A024899 which are not in A002822. %H A121765 G. C. Greubel, <a href="/A121765/b121765.txt">Table of n, a(n) for n = 1..10000</a> %t A121765 Select[Range[250], ! PrimeQ[6# - 1] && PrimeQ[6# + 1] &] (* _Ray Chandler_, Aug 22 2006 *) %o A121765 (PARI) for(n=1, 250, if(!isprime(6*n-1) && isprime(6*n+1), print1(n", "))) \\ _G. C. Greubel_, Feb 20 2019 %o A121765 (Magma) [n: n in [1..250] | not IsPrime(6*n-1) and IsPrime(6*n+1)]; // _G. C. Greubel_, Feb 20 2019 %o A121765 (Sage)[n for n in (1..250) if not is_prime(6*n-1) and is_prime(6*n+1)] # _G. C. Greubel_, Feb 20 2019 %o A121765 (GAP) Filtered([1..250], k-> not IsPrime(6*k-1) and IsPrime(6*k+1)); # _G. C. Greubel_, Feb 20 2019 %Y A121765 Cf. A121764. %K A121765 nonn %O A121765 1,1 %A A121765 _Lekraj Beedassy_, Aug 20 2006 %E A121765 Extended by _Ray Chandler_, Aug 22 2006