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 A172437 Indices of pentagonal pyramidal numbers which are the sum of two other such numbers: k such that A002411(k) = A002411(i)+A002411(j) for some i,j>0. 2

%I

%S 42,82,171,411,522,886,1042,1066,1183,1341,2596,2842,3480,3831,5012,

%T 5316,5360,5786,6219,6650,6924,8406,8666,9408,10707,11735,12590,12891,

%U 14422,14646,14826,17351,17702,17757,18882,23210,24108,25127,28175,31980,32400

%N Indices of pentagonal pyramidal numbers which are the sum of two other such numbers: k such that A002411(k) = A002411(i)+A002411(j) for some i,j>0.

%C The numbers themselves are listed in A172425. This answers a question posed in A133459.

%H Donovan Johnson, <a href="/A172437/b172437.txt">Table of n, a(n) for n = 1..160</a>

%e a(1)=42 because A002411(42) is the smallest term in that sequence which is the sum of two other (nonzero) terms of A002411.

%o (PARI) for(n=1,99999,for(m=1,n-1, isA002411(p(n)-p(m)) & !print1(n", ") & break)) /* needs isA002411() and p() */

%Y Cf. A133459, A172425.

%K nonn

%O 1,1

%A _M. F. Hasler_, Nov 20 2010

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