1,2

The associated numbers of A000217(j) are j=1,4,14,45,454,4654,46545,1474670,... for n=1,2,3,... - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 20 2006

buffedStr := proc(n, candid) local f ; if length(n) = 0 then RETURN(true) ; fi ; f := SearchText(substring(n, 1), candid) ; if f = 0 then RETURN(false) ; else if buffedStr(substring(n, 2..-1), substring(candid, f+1..-1)) = true then RETURN(true) ; else RETURN(false) ; fi ; fi ; end: A000217 := proc(n) RETURN(n*(n+1)/2) ; end: A068618 := proc(preva) local trilo, tri ; trilo := floor(evalf(-preva/2+sqrt(preva*preva/4+preva))) ; while evalf(A000217(trilo)) <= evalf(preva) do trilo := trilo+1 ; od: while true do tri := A000217(trilo) ; if buffedStr(convert(preva, string), convert(tri, string)) = true then RETURN(tri) ; fi ; trilo := trilo+1 ; od: end: an :=1 ; for n from 2 to 15 do an := A068618(an) ; end ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 20 2006

(PARI) { anext(n) = s=eval(Vecrev(Str(n))); d=1; r=[]; while(!#r, forvec(v=vector(d, i, [1, #s+d]), forvec(u=vector(d, i, [0, 9]), k=1; t=sum(j=1, #s+d, 10^(j-1) * if(k<=d&&j==v[k], k++; u[k-1], s[j-k+1]) ); if(t!=n&&issquare(8*t+1), r=concat(r, [t])); ), 2); d++); vecmin(r) } [From Max Alekseyev (maxale(AT)gmail.com), Apr 21 2009]

Sequence in context: A117833 A068093 A077369 this_sequence A096484 A004343 A163166

Adjacent sequences: A068615 A068616 A068617 this_sequence A068619 A068620 A068621

base,hard,more,nonn

Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Feb 25 2002

3 more terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 20 2006

One more term Max Alekseyev (maxale(AT)gmail.com), Apr 21 2009