One of the properties of today's number 26618, that marks my diurnal age, is that it is a member of OEIS A100206:
A100206 | Row sums of Clark's triangle A046902: Clark's triangle: left border = 0 1 1 1..., right border = multiples of 6; other entries = sum of 2 entries above. |
The setup is shown in Figure 1, although it is a mirror image of that described in OEIS A100206 because the borders are reversed. The significance of the (m−1)2 and the n2 will be explained shortly.
Figure 1: source |
Clark's triangle is a number triangle created by setting the vertex equal to 0, filling one diagonal with 1s, the other diagonal with multiples of an integer f, and filling in the remaining entries by summing the elements on either side from one row above. Figure 1 above shows Clark's triangle for f=6.
Call the first column n=0 and the last column m=n so that:cm0=fmcmm=1then use the recurrence relationcmn=cm−1,n−1+cm−1,nto compute the rest of the entries. The result is given analytically bycmn=f×(mn+1)+(m−1n−1)where (nk) is a binomial coefficient.
The interesting part is that if f=6 is chosen as the integer, thencm2 and cm3 simplify tocm2=(m−1)3cm3=(m−1)2(m−2)24which are consecutive cubes (m−1)3 and nonconsecutive squaresn2=((m−1)(m−2)2)2The sum of the m-th row for m>0 is given bym∑n=0cmn=2m−1+f×(2m−1)(M. Alekseyev, pers. comm., Aug. 10, 2005).
The row sums (of which 26618 is a member and where f=6) are as follows:
0, 7, 20, 46, 98, 202, 410, 826, 1658, 3322, 6650, 13306, 26618, 53242, 106490, 212986, 425978, 851962, 1703930, 3407866, 6815738, 13631482, 27262970, 54525946, 109051898, 218103802, 436207610, 872415226, 1744830458, 3489660922
Of course there are as many sequences as there are different values of f but none is listed in the OEIS apart from A100206 where f=6. In all sequences, the ratio of successive terms rapidly approaches 2.
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