A156871
Number of nondecreasing sequences of n positive integers with reciprocals adding up to an integer.
Original entry on oeis.org
1, 2, 5, 20, 170, 3650, 298132, 159632503
Offset: 1
For n = 3, the A156871(3) = 5 sequences are (1, 1, 1), (1, 2, 2), (2, 3, 6), (2, 4, 4) and (3, 3, 3) because 1/1 + 1/1 + 1/1 = 3, 1/1 + 1/2 + 1/2 = 2 and 1/2 + 1/3 + 1/6 = 1/2 + 1/4 + 1/4 = 1/3 + 1/3 + 1/3 = 1.
A280518
Number of increasing sequences of n positive integers with reciprocals adding up to an integer.
Original entry on oeis.org
1, 0, 1, 7, 78, 2392, 248085, 151428144
Offset: 1
a(4)=7 enumerates sequences: (1,2,3,6), (2,4,5,20), (2,4,6,12), (2,3,7,42), (2,3,8,24), (2,3,9,18), and (2,3,10,15).
A280519
Triangle read by rows: T(n,k) = number of sequences of n positive integers with reciprocals adding up to k (k=1,2,...,n).
Original entry on oeis.org
1, 1, 1, 10, 3, 1, 215, 41, 6, 1, 12231, 1115, 105, 10, 1, 2025462, 74862, 3466, 215, 15, 1, 1351857641, 14294210, 267281, 8372, 385, 21, 1, 6255560531733, 10837663111, 57646358, 727049, 17318, 630, 28, 1
Offset: 1
Triangle starts with:
n=1: 1
n=2: 1, 1
n=3: 10, 3, 1
n=4: 215, 41, 6, 1
n=5: 12231, 1115, 105, 10, 1
n=6: 2025462, 74862, 3466, 215, 15, 1
...
Showing 1-3 of 3 results.