cp's OEIS Frontend

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.

A108219 Numbers n such that A001414(n) is a golden semiprime, where A001414 is the sum of primes dividing n (with repetition).

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%I A108219 #11 Nov 29 2019 04:01:58
%S A108219 8,9,26,44,105,112,125,126,150,160,180,192,216,243,292,568,639,1174,
%T A108219 1407,1448,1629,1675,2010,2144,2379,2412,2685,2722,2864,3222,3355,
%U A108219 3835,3999,4026,4107,4543,4602,5035,5709,5978,6042,6235,6307,6355,6490,7482
%N A108219 Numbers n such that A001414(n) is a golden semiprime, where A001414 is the sum of primes dividing n (with repetition).
%C A108219 Numbers n such that A001414(n) and A001414(n+1) are both golden semiprimes: 8, 125, 153759, 247455, 678807, 1243499, 1243500, ... Notice that the last two terms indicate a triple. Conjecture: this subsequence is infinite.
%H A108219 Amiram Eldar, <a href="/A108219/b108219.txt">Table of n, a(n) for n = 1..10000</a>
%e A108219 5709 = 3*11*173 is in the sequence because 3+11+173 = 187 = 11*17 and 11*phi-17 = 0.79837... < 1.
%t A108219 goldQ[n_] := Module[{f = FactorInteger[n]}, If[Length[f] != 2, False, If[Max[f[[;;,2]]] != 1, False, Abs[f[[2,1]] - f[[1,1]] * GoldenRatio] < 1]]]; sumPrimes[n_] := Plus @@ Times @@@ FactorInteger[n]; Select[Range[7500], goldQ[sumPrimes[#]] &] (* _Amiram Eldar_, Nov 29 2019 *)
%Y A108219 Cf. A001414, A108540.
%K A108219 nonn
%O A108219 1,1
%A A108219 _Jason Earls_, Jun 16 2005