cp's OEIS Frontend

A065221 Fill a triangular array by rows by writing numbers 1 up to b(0), 1 up to b(1), etc., where b(n) are the pentagonal numbers. The final elements of the rows form a(n).

%I A065221 #7 Nov 01 2024 15:01:56
%S A065221 1,2,5,4,9,3,10,18,5,15,26,3,16,30,45,10,27,45,64,14,35,57,80,12,37,
%T A065221 63,90,1,30,60,91,123,11,45,80,116,153,15,54,94,135,177,10,54,99,145,
%U A065221 192,240,42,92,143,195,248,15,70,126,183,241,300,30,91,153,216,280,345,35
%N A065221 Fill a triangular array by rows by writing numbers 1 up to b(0), 1 up to b(1), etc., where b(n) are the pentagonal numbers. The final elements of the rows form a(n).
%e A065221 The array begins
%e A065221 ....1
%e A065221 ...1.2
%e A065221 ..3.4.5
%e A065221 .1.2.3.4
%e A065221 5.6.7.8.9
%Y A065221 Cf. A000326.
%Y A065221 Mini-index to these sequences: A064766, A064865, A064866, A065221-A655234 are all of the same type. See A064766 for a detailed explanation.
%K A065221 easy,nonn
%O A065221 0,2
%A A065221 _Floor van Lamoen_, Oct 22 2001