login
Numbers k such that k^2 + (k+1)^2 is palindromic.
3

%I #32 Jun 01 2021 03:12:45

%S 0,1,9,12,16,919,1257,1262,1621,1706,170706,904280,1258182,7901014,

%T 8659929,12458597,17070706,80472264,1616689803,1680689788,1705387643,

%U 7360311900,8032814139,8055329360,12574461617,16794058711,165058650666,844706005220,1250999800012,1255589965852

%N Numbers k such that k^2 + (k+1)^2 is palindromic.

%C a(50) > 70710678118654752440. - _Patrick De Geest_, May 25 2021

%H Patrick De Geest, <a href="/A027571/b027571.txt">Table of n, a(n) for n = 1..49</a> (terms a(1)..a(29) from Giovanni Resta)

%H Patrick De Geest, <a href="http://www.worldofnumbers.com/sumsquare.htm">Palindromic Sums of Squares of Consecutive Integers</a>

%H Patrick De Geest, <a href="http://www.worldofnumbers.com/centered.htm">Palindromic Centered Polygonal Numbers</a>

%o (PARI) isok(m) = my(d=digits(m^2+(m+1)^2)); d == Vecrev(d); \\ _Michel Marcus_, Jan 05 2019

%Y Cf. A001844, A027572, A050236, A050239.

%Y A050236 is a subsequence.

%K nonn,base

%O 1,3

%A _Patrick De Geest_

%E a(18)-a(21) from _Donovan Johnson_, Aug 26 2012

%E a(22)-a(29) from _Giovanni Resta_, Aug 06 2019

%E a(1)=0 added by _Patrick De Geest_, May 25 2021