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A115682 Triangular numbers whose digit reversal is a pentagonal number (A000326). 0

%I #10 Apr 16 2014 05:37:41

%S 1,10,15,21,210,62481,67896,557040,2618616,10095771,10550121,28883800,

%T 62490610,1524872700,2708516800,5491258003,103352174628,299536839001,

%U 24709216250400,7220385308804403,7686108558349885,10917127849295955,15038347789610970,23424201805125660

%N Triangular numbers whose digit reversal is a pentagonal number (A000326).

%e 62481=T(353) and 18426 is the 111th pentagonal number.

%o (PARI) lista(nn) = {for(n=1, nn, t = n*(n+1)/2; if (ispolygonal(subst(Polrev(digits(t)), x, 10), 5), print1(n*(n+1)/2, ", ")););} \\ _Michel Marcus_, Apr 16 2014

%Y Cf. A000326.

%K nonn,base

%O 1,2

%A _Giovanni Resta_, Jan 31 2006

%E a(19)-a(24) from _Michel Marcus_, Apr 16 2014

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Last modified March 29 00:26 EDT 2024. Contains 371264 sequences. (Running on oeis4.)