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A198277 a(n) is the smallest prime such that exactly n prime pairs (p,q) exist with a(n) = p * q + p + q.

%I A198277 #19 Apr 07 2020 21:07:46
%S A198277 2,11,23,71,239,719,2879,5039,1439,10079,37799,126719,55439,110879,
%T A198277 181439,191519,166319,635039,514079,665279,1330559,907199,3243239,
%U A198277 831599,2948399,6320159,4989599,15301439,14137199,5266799,11531519,8315999,23284799,17463599,45208799,52390799,34594559,111767039,95633999,117976319,70685999,68468399
%N A198277 a(n) is the smallest prime such that exactly n prime pairs (p,q) exist with a(n) = p * q + p + q.
%C A198277 A067432(A049084(a(n))) = n and A067432(A049084(m)) <> n for m < a(n).
%H A198277 Charles R Greathouse IV, <a href="/A198277/b198277.txt">Table of n, a(n) for n = 0..115</a>
%H A198277 Reinhard Zumkeller, <a href="/A198277/a198277.txt">Illustration of initial terms</a>
%o A198277 (Haskell)
%o A198277 import Data.List (elemIndex)
%o A198277 import Data.Maybe (fromJust)
%o A198277 a198277 n = a000040 . (+ 1) . fromJust $ elemIndex n a067432_list
%o A198277 (PARI) ct(n)=sumdiv(n+1,d,if(d^2>n,0, isprime(d-1)&&isprime(n\d)))
%o A198277 v=vector(60);forprime(p=2,1e9, t=ct(p);if(t && !v[t], v[t]=p; print(t" "p))); v \\ with 0's for unknown; _Charles R Greathouse IV_, Jul 24 2013
%K A198277 nonn
%O A198277 0,1
%A A198277 _Reinhard Zumkeller_, Oct 23 2011
%E A198277 a(27)-a(33) from _Donovan Johnson_, Oct 24 2011
%E A198277 a(34)-a(41) from _Charles R Greathouse IV_, Jul 24 2013