A069692 - OEIS

%I #12 Sep 23 2022 11:58:05

%S 105,210,120,136,741,153,465,171,780,190,6105,0,1128,30135,2145,5151,

%T 3160,1176,4186,0,80200,2211,1225,0,3240,5253,7260,1275,0,10296,20301,

%U 9316,1326,700336,2346,5356,0,1378,7381,0,3403,2415,0,1431,6441,9453

%N Smallest triangular number with value of the internal digits = n; or 0 if no such number exists.

%C Subset of A000217. - _R. J. Mathar_, Apr 07 2006

%e a(13) = 30135 as the internal digits are 013 with value 13.

%p midl := proc(n) local nshf,resul,dig ; resul := 0 ; dig := 0 ; nshf := iquo(n,10) ; while nshf >= 10 do resul := 10^dig* irem(nshf,10)+resul ; nshf := iquo(nshf,10) ; dig := dig+1 ; od ; RETURN(resul) ; end: for n from 1 to 40 do for t from 1 to 1000000 do tri := t*(t+1)/2 ; if midl(tri) = n then printf("%a,",tri) ; break ; elif t = 1000000 then printf("0,") ; fi ; od: od : # _R. J. Mathar_, Apr 07 2006

%Y Cf. A000217, A069691.

%K nonn,base

%O 0,1

%A _Amarnath Murthy_, Apr 06 2002

%E Corrected and extended by _R. J. Mathar_, Apr 07 2006