A337047 - OEIS

%I #15 Feb 06 2021 21:59:27

%S 405,412,850,25315,49419,50127,224315,293394,308700,697136,801350,

%T 811910,997425,1118520,1152000,1177250,1550520,1659350,1725332,

%U 1739640,1824500,1976895,2141150,2580640,2580831,3530466,3718376,4050405,4459455,4536532,4577732,4832796,5173100,5510287,5601570,5603989,5609439

%N Numbers k such that A001414(k) and A001414(A004086(k)) are twin primes p, p+2.

%H Robert Israel, <a href="/A337047/b337047.txt">Table of n, a(n) for n = 1..150</a>

%e a(3)=850 is in the sequence because A001414(850)=2+5+5+17=29, A001414(58)=2+29=31, and (29,31) is a pair of twin primes.

%p revdigs:= proc(n) local L,k;

%p   L:= convert(n,base,10);

%p   add(L[-k]*10^(k-1),k=1..nops(L))

%p end proc:

%p filter:= proc(n) local a,b;

%p   a:= convert(map(convert,ifactors(n)[2],`*`),`+`);

%p   if not isprime(a) then return false fi;

%p   b:= convert(map(convert,ifactors(revdigs(n))[2],`*`),`+`);

%p   b = a+2 and isprime(b)

%p end proc:

%p select(filter, [$1 .. 10^7]);

%Y Cf. A001097, A001414, A004086. Subsequence of A100118.

%K nonn,base

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Aug 12 2020