A337047 Numbers k such that A001414(k) and A001414(A004086(k)) are twin primes p, p+2.

405, 412, 850, 25315, 49419, 50127, 224315, 293394, 308700, 697136, 801350, 811910, 997425, 1118520, 1152000, 1177250, 1550520, 1659350, 1725332, 1739640, 1824500, 1976895, 2141150, 2580640, 2580831, 3530466, 3718376, 4050405, 4459455, 4536532, 4577732, 4832796, 5173100, 5510287, 5601570, 5603989, 5609439

Offset: 1

Author

J. M. Bergot and Robert Israel, Aug 12 2020

Keywords

• nonn
• base

Examples

			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.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..150

Crossrefs

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

Programs

Maple

revdigs:= proc(n) local L,k;
  L:= convert(n,base,10);
  add(L[-k]*10^(k-1),k=1..nops(L))
end proc:
filter:= proc(n) local a,b;
  a:= convert(map(convert,ifactors(n)[2],`*`),`+`);
  if not isprime(a) then return false fi;
  b:= convert(map(convert,ifactors(revdigs(n))[2],`*`),`+`);
  b = a+2 and isprime(b)
end proc:
select(filter, [$1 .. 10^7]);