|
%I #9 Jan 22 2019 17:30:46
%S 1,3,7,77,99,151,161,333,707,727,737,757,949,969,989,1441,1551,1771,
%T 1881,3003,7227,7667,7997,9009,9339,9999,10001,10101,10701,11111,
%U 11611,11711,12221,12921,13231,14341,14841,14941,15851,16661,16961,17071
%N Concatenation of palindrome k and its 10's complement is prime.
%C Contains 10^k-1 for k in A056696, and (10^k-1)/9 for k in A108966. - _Robert Israel_, Jan 22 2019
%H Robert Israel, <a href="/A108537/b108537.txt">Table of n, a(n) for n = 1..10000</a>
%e a(7)=161 because 1000-161 = 839 and 161839 is prime.
%p N:= 5: # for terms of <= N digits
%p digrev:= proc(n) local L,i;
%p L:= convert(n,base,10);
%p add(L[-i]*10^(i-1),i=1..nops(L))
%p end proc:
%p Res:= 1,3,7,9:
%p for d from 2 to N do
%p if d::even then
%p m:= d/2;
%p Res:= Res, seq(seq((i*10^(m-1)+j)*10^m + digrev(i*10^(m-1)+j), j=0..10^(m-1)-1),i=[1,3,7,9]);
%p else
%p m:= (d-1)/2;
%p Res:= Res, seq(seq(seq((i*10^(m-1)+j)*10^(m+1)+y*10^m+digrev(i*10^(m-1)+j), y=0..9), j=0..10^(m-1)-1),i=[1,3,7,9]);
%p fi
%p od:
%p filter:= proc(t) local r;
%p r:= 10^(ilog10(t)+1)-t;
%p isprime(t*10^(ilog10(r)+1)+r)
%p end proc:
%p select(filter, [Res]); # _Robert Israel_, Jan 22 2019
%Y Cf. A056696, A108966.
%K base,easy,nonn
%O 1,2
%A _Jason Earls_, Jul 25 2005
|
