This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A087597 #21 Aug 27 2024 22:17:11
%S A087597 0,1,3,6,10,21,28,36,45,55,66,78,105,171,465,528,561,666,2211,4465,
%T A087597 7503,16836,18336,22791,44850,53628,55278,82621,105111,114003,333336,
%U A087597 427350,828828,2220778,2256750,3136260,3373503,3454506,3927003,5443350,6175855,7552441
%N A087597 Triangular numbers m such that A040115(m) is also triangular.
%C A087597 Conjecture: Sequence is infinite.
%H A087597 Robert Israel, <a href="/A087597/b087597.txt">Table of n, a(n) for n = 1..100</a>
%e A087597 171 is a member as A040115(171) = 66 is also a triangular number.
%p A087597 q:= n-> issqr(1+8*(l-> parse(cat(0,seq(abs(l[-i]-l[1-i])
%p A087597 , i=2..nops(l)))))(convert(n, base, 10))):
%p A087597 select(q, [i*(i+1)/2$i=0..10000])[]; # _Alois P. Heinz_, Jul 27 2024
%o A087597 (PARI) dd(k)={ local(kshf,res,dig,odig,p) ; kshf=k ; res=0 ; odig=kshf % 10 ; p=0 ; while(kshf>9, kshf=floor(kshf/10) ; dig=kshf % 10 ; res += 10^p*abs(dig-odig) ; odig=dig ; p++ ; ) ; return(res) ; } isA000217(n)={ if( issquare(1+8*n), return(1), return(0) ) ; } isA087597(n)={ if( isA000217(n) && isA000217(dd(n)), return(1), return(0) ) ; } { for(k=10,10000000, if(isA087597(k), print1(k,",") ; ) ; ) ; } \\ _R. J. Mathar_, Nov 19 2006
%Y A087597 Cf. A000217, A040115, A087598, A087599, A087600.
%K A087597 base,nonn
%O A087597 1,3
%A A087597 _Amarnath Murthy_, Sep 18 2003
%E A087597 Corrected and extended by _R. J. Mathar_, Nov 19 2006
%E A087597 Definition clarified, offset corrected, and terms 0,1,3,6 prepended by _Max Alekseyev_, Jul 27 2024