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A048210 T(n,1) + T(n,n), array T given by A048201.

%I A048210 #18 Sep 02 2025 18:21:39
%S A048210 2,5,11,17,28,40,58,74,91,117,140,168,195,225,263,298,334,371,411,453,
%T A048210 497,547,597,647,698,754,815,878,942,1008,1074,1149,1233,1316,1398,
%U A048210 1483,1570,1657,1751,1843,1936,2044,2152,2262,2371
%N A048210 T(n,1) + T(n,n), array T given by A048201.
%H A048210 Chai Wah Wu, <a href="/A048210/b048210.txt">Table of n, a(n) for n = 1..10000</a>
%F A048210 a(n) = 2*A004978(n+1) - A004978(n) - 1. - _Sean A. Irvine_, Jun 05 2021
%o A048210 (Python)
%o A048210 from itertools import count, accumulate, islice
%o A048210 from collections import deque
%o A048210 def A048210_gen(): # generator of terms
%o A048210     aset, alist, c = set(), deque(), 0
%o A048210     for k in count(1):
%o A048210         if k in aset:
%o A048210             aset.remove(k)
%o A048210         else:
%o A048210             yield (c:=c+k)+k
%o A048210             aset |= set(k+d for d in accumulate(alist))
%o A048210             alist.appendleft(k)
%o A048210 A048210_list = list(islice(A048210_gen(),45)) # _Chai Wah Wu_, Sep 02 2025
%Y A048210 Cf. A048201, A004978.
%K A048210 nonn,changed
%O A048210 1,1
%A A048210 _Clark Kimberling_