A344871 - OEIS

%I #12 Jun 01 2021 02:15:54

%S 1,4,44,88,1090,3212,4334,2992,5995,4994,7997,9779,5104,11110,11891,

%T 10109,11000,10780,108880,110500,252142,278872,296692,293282,308902,

%U 287782,411103,289982,466664,281072,457754,398893,298892,462154,517814,494384,299992,707806,471064,476674,487784,467764

%N a(n) is the least number that can be represented in exactly n ways as the sum of a prime and its digit reversal.

%C If the reversal of p is another prime, p+reversal(p) and reversal(p)+p are both counted.

%C a(n) is the first number that occurs exactly n times in A061227.

%H Robert Israel, <a href="/A344871/b344871.txt">Table of n, a(n) for n = 0..92</a>

%e a(4) = 1090 because 1090 = 149+941 = 347+743 = 743+347 = 941+149, and this is the least number with exactly four such representations.

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

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

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

%p end proc:

%p V:= Vector(10^6):

%p p:= 1:

%p do

%p   p:= nextprime(p);

%p   if p > 9*10^5 then break fi;

%p   r:= p+revdigs(p);

%p   if r <= 10^6 then V[r]:= V[r]+1 fi

%p od:

%p A:= Array(0..64):

%p for i from 1 to 10^6 do

%p   if V[i] <= 64 and A[V[i]] = 0 then A[V[i]]:= i fi

%p od:

%p convert(A,list);

%Y Cf. A004086, A061227, A056964.

%K nonn,base

%O 0,2

%A _J. M. Bergot_ and _Robert Israel_, May 31 2021