login
Numbers n such that no substring is a triangular number.
1

%I #8 Aug 18 2024 20:11:04

%S 2,4,5,7,8,9,22,24,25,27,29,42,44,47,48,49,52,54,57,58,59,72,74,75,77,

%T 79,82,84,85,87,88,89,92,94,95,97,98,99,222,224,225,227,229,242,244,

%U 247,248,249,252,254,257,258,259,272,274,275,277,279,292,294,295,297

%N Numbers n such that no substring is a triangular number.

%H Robert Israel, <a href="/A062102/b062102.txt">Table of n, a(n) for n = 1..10000</a>

%e 23 is not included because 3 is triangular

%p istri:= n -> issqr(1+8*n):

%p filter:= proc(n) local d,i,j,v;

%p for i from 0 do

%p v:= floor(n/10^i);

%p if v = 0 then return true fi;

%p if istri(v) then return false fi;

%p for j from ilog10(v) to 1 by -1 do

%p if istri(v mod 10^j) then return false fi;

%p od

%p od

%p end proc:

%p select(filter, [$1..1000]); # _Robert Israel_, Aug 18 2024

%K base,easy,nonn

%O 1,1

%A _Erich Friedman_, Jun 28 2001