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A094890 Triangular numbers whose sum of squared digits is also triangular. 1

%I

%S 0,1,6,10,36,630,741,1081,2211,7140,10011,10153,13366,15576,17766,

%T 23220,24531,25651,28920,33411,42486,47586,52326,59685,61776,69006,

%U 112575,113050,121771,125751,128778,129286,146611,156520,163306,165025,167331

%N Triangular numbers whose sum of squared digits is also triangular.

%H Amiram Eldar, <a href="/A094890/b094890.txt">Table of n, a(n) for n = 1..10000</a>

%p isA094890 := proc(n)

%p if isA000217(n) and isA000217(A003132(n)) then

%p true;

%p else

%p false;

%p end if;

%p end proc:

%p for n from 0 to 300 do

%p T := A000217(n) ;

%p if isA094890(T) then

%p printf("%d,",T) ;

%p end if;

%p end do: # _R. J. Mathar_, Nov 15 2019

%t tri[n_] := n (n + 1)/2; triQ[n_] := IntegerQ @ Sqrt[8 n + 1]; sumSqDig[n_] := Total @ (IntegerDigits[n]^2); aQ[n_] := triQ @ sumSqDig @ tri[n]; tri /@ Select[Range[0, 578], aQ] (* _Amiram Eldar_, Dec 23 2019 *)

%Y Cf. A003132.

%K base,nonn

%O 1,3

%A _Jason Earls_, Jun 16 2004

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Last modified August 8 11:12 EDT 2020. Contains 336293 sequences. (Running on oeis4.)