A178190
Sum 7^((k^2+3k)/2) from k=1 to n.
Original entry on oeis.org
49, 16856, 40370463, 678263443312, 79792944561055313, 65712442156478841194856, 378818757978106938161558820799, 15286701010761334171872123930835647200
Offset: 1
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A178190:=n->add(7^((k^2 + 3*k)/2), k=1..n); seq(A178190(n), n=1..10); # Wesley Ivan Hurt, Apr 01 2014
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aa = {}; m = 7; sum = 0; Do[sum = sum + m^((n + 3) n/2); AppendTo[aa, sum], {n, 1, 20}]; aa (* Artur Jasinski *)
Table[Sum[7^((k^2 + 3 k)/2), {k, n}], {n, 10}] (* Wesley Ivan Hurt, Apr 01 2014 *)
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a(n) = sum(k=1, n, 7^((k^2+3*k)/2)); \\ Michel Marcus, Sep 09 2013
A178191
Numerators of sum (1/7)^((k^2+3k)/2) from k=1 to n.
Original entry on oeis.org
1, 344, 825945, 13881657616, 1633163136864785, 1344980069223035633256, 7753542448037025041629822057, 312883404805904029979088478768109600, 88381817680515537538446482833052972519290401
Offset: 1
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aa = {}; m = 1/7; sum = 0; Do[sum = sum + m^((n + 3) n/2); AppendTo[aa, Numerator[sum]], {n, 1, 20}]; aa (*Artur Jasinski*)
Numerator[Accumulate[Table[(1/7)^((n^2+3n)/2),{n,10}]]] (* Harvey P. Dale, Jul 21 2016 *)
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a(n) = numerator(sum(k=1, n, (1/7)^((k^2+3*k)/2))); \\ Michel Marcus, Sep 09 2013
A178192
Sum 11^((k^2+3k)/2) from k=1 to n.
Original entry on oeis.org
121, 161172, 2358108863, 379752191692104, 672750374684751701305, 13109994864250305051813161676, 2810243697916419649311518955166566527, 6626407610546884801816680266380777080570215568
Offset: 1
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aa = {}; m = 11; sum = 0; Do[sum = sum + m^((n + 3) n/2); AppendTo[aa, sum], {n, 1, 20}]; aa (*Artur Jasinski*)
Table[11^((k^2+3k)/2),{k,10}]//Accumulate (* Harvey P. Dale, Apr 02 2020 *)
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a(n) = sum(k=1, n, 11^((k^2+3*k)/2)); \\ Michel Marcus, Sep 09 2013
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