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A172437
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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.
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2
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42, 82, 171, 411, 522, 886, 1042, 1066, 1183, 1341, 2596, 2842, 3480, 3831, 5012, 5316, 5360, 5786, 6219, 6650, 6924, 8406, 8666, 9408, 10707, 11735, 12590, 12891, 14422, 14646, 14826, 17351, 17702, 17757, 18882, 23210, 24108, 25127, 28175, 31980, 32400
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OFFSET
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1,1
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COMMENTS
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The numbers themselves are listed in A172425. This answers a question posed in A133459.
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LINKS
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EXAMPLE
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a(1)=42 because A002411(42) is the smallest term in that sequence which is the sum of two other (nonzero) terms of A002411.
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PROG
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(PARI) for(n=1, 99999, for(m=1, n-1, isA002411(p(n)-p(m)) & !print1(n", ") & break)) /* needs isA002411() and p() */
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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