cp's OEIS Frontend

A340633 Primes of the form k + A037276(k).

%I A340633 #17 Feb 06 2021 22:09:26
%S A340633 2,29,41,233,239,251,257,269,293,311,359,383,401,419,449,467,491,2269,
%T A340633 2309,2339,2377,2381,2393,2411,2417,2447,2473,2503,2543,2579,2591,
%U A340633 2621,2633,2671,2687,2699,2713,2753,2789,2797,2819,2843,2879,2939,3011,3041,3067,3083,3119,3137,3167,3191,3203
%N A340633 Primes of the form k + A037276(k).
%C A340633 All terms have first digit 2, 3 or 4.
%H A340633 Robert Israel, <a href="/A340633/b340633.txt">Table of n, a(n) for n = 1..10000</a>
%e A340633 a(1) =   2 =  1 + A037276(1)  =  1 +   1;
%e A340633 a(2) =  29 =  6 + A037276(6)  =  6 +  23;
%e A340633 a(3) =  41 = 14 + A037276(14) = 14 +  27;
%e A340633 a(4) = 233 = 22 + A037276(22) = 22 + 211;
%e A340633 a(5) = 251 = 18 + A037276(18) = 18 + 233
%e A340633            = 34 + A037276(34) = 34 + 217.
%p A340633 N:= 5000: # for terms <= N
%p A340633 dcat:= proc(L) local i, x;
%p A340633   x:= L[-1];
%p A340633   for i from nops(L)-1 to 1 by -1 do
%p A340633     x:= 10^(1+ilog10(x))*L[i]+x
%p A340633   od;
%p A340633   x
%p A340633 end proc:
%p A340633 A037276:= proc(n) local F;
%p A340633   F:= sort(ifactors(n)[2], (a, b) -> a[1] < b[1]);
%p A340633   dcat(map(t -> t[1]$t[2], F));
%p A340633 end proc:
%p A340633 A037276(1):= 1:
%p A340633 R:= NULL:
%p A340633 for n from 1 to N/2 do
%p A340633   v:= n + A037276(n);
%p A340633   if v < N and isprime(v) then R:= R, v fi;
%p A340633 od:
%p A340633 sort(convert({R},list));
%Y A340633 Cf. A037276, A340634, A340636.
%K A340633 nonn,look,base
%O A340633 1,1
%A A340633 _J. M. Bergot_ and _Robert Israel_, Jan 13 2021