cp's OEIS Frontend

A340636 Primes of the form k + A037276(k) in more than one way.

%I A340636 #13 Feb 06 2021 22:09:47
%S A340636 251,2671,2687,2753,23327,23561,27827,28499,28789,28817,29411,34757,
%T A340636 223441,226001,227537,230849,231359,232217,232259,232367,232643,
%U A340636 232919,233591,234791,236129,236609,236867,237857,238141,239023,239873,240899,241169,241343,241687,241691,242447,242747,245299
%N A340636 Primes of the form k + A037276(k) in more than one way.
%H A340636 Robert Israel, <a href="/A340636/b340636.txt">Table of n, a(n) for n = 1..7500</a>
%e A340636 a(3) = 2687 = 170 + A037276(170) = 170 + 2517
%e A340636             = 458 + A037276(458) = 458 + 2229.
%e A340636 The first term that occurs in more than two ways is
%e A340636 a(163) = 2255299 =  4180 + A037276(4180)  =  4180 + 2251119
%e A340636                  = 21156 + A037276(21156) = 21156 + 2234143
%e A340636                  = 29560 + A037276(29560) = 29560 + 2225739.
%p A340636 N:= 5*10^5: # for terms <= N
%p A340636 dcat:= proc(L) local i, x;
%p A340636   x:= L[-1];
%p A340636   for i from nops(L)-1 to 1 by -1 do
%p A340636     x:= 10^(1+ilog10(x))*L[i]+x
%p A340636   od;
%p A340636   x
%p A340636 end proc:
%p A340636 A037276:= proc(n) local F;
%p A340636   F:= sort(ifactors(n)[2], (a, b) -> a[1] < b[1]);
%p A340636   dcat(map(t -> t[1]$t[2], F));
%p A340636 end proc:
%p A340636 A037276(1):= 1:
%p A340636 R:= NULL:
%p A340636 for n from 1 to N/2 do
%p A340636   v:= n + A037276(n);
%p A340636   if v < N and isprime(v) then R:= R, v fi;
%p A340636 od:
%p A340636 S:= {R}:
%p A340636 select(s -> numboccur(s,[R])>1, S);
%Y A340636 Cf. A037276, A340633, A340634.
%K A340636 nonn,base
%O A340636 1,1
%A A340636 _J. M. Bergot_ and _Robert Israel_, Jan 14 2021