A108537 Concatenation of palindrome k and its 10's complement is prime.
1, 3, 7, 77, 99, 151, 161, 333, 707, 727, 737, 757, 949, 969, 989, 1441, 1551, 1771, 1881, 3003, 7227, 7667, 7997, 9009, 9339, 9999, 10001, 10101, 10701, 11111, 11611, 11711, 12221, 12921, 13231, 14341, 14841, 14941, 15851, 16661, 16961, 17071
Offset: 1
Examples
a(7)=161 because 1000-161 = 839 and 161839 is prime.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Maple
N:= 5: # for terms of <= N digits digrev:= proc(n) local L,i; L:= convert(n,base,10); add(L[-i]*10^(i-1),i=1..nops(L)) end proc: Res:= 1,3,7,9: for d from 2 to N do if d::even then m:= d/2; 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]); else m:= (d-1)/2; 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]); fi od: filter:= proc(t) local r; r:= 10^(ilog10(t)+1)-t; isprime(t*10^(ilog10(r)+1)+r) end proc: select(filter, [Res]); # Robert Israel, Jan 22 2019
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