[seqfan] Re: help with a sequence
Bob Selcoe
rselcoe at entouchonline.net
Fri Aug 5 11:54:33 CEST 2016
Hi Jamie,
Ok, if I understand correctly, what you're saying is when (prime(i) - prime
(j))/2 is prime, then the most ways to express n = (prime(i) + prime(j))/2
is when n = primorial(k)? But that doesn't hold for 6 and 30. And it seems
like there are a lot of counter-examples for a(n) being relatively large
when n has a relatively large number of unique primes.
Do you mean, rather, that there tend to be peaks when n is a multiple of
primorial(k), and the peaks amplify as k increases? The first graph
certainly suggests that may be the case. If so, I would definitely
recommend adding your sequence {0,0,0,0,0,1,0,0,2,1,2,0,2...} i.e., a(n) is
the number of ways to express n = (prime(i) + prime(j))/2 when (prime(i) -
prime (j))/2 also is prime. (Perhaps there's a better name for it).
BTW - what is the next prime n after a(5) where a(n) > 0?
Cheers,
Bob S
____
> > Now if you ask the question how many of these equations does a given
> centerpoint have, then that is what the significance would be since it
> shows
> that there are peaks in the centerpoint count on numbers that have the
> most
> unique prime factors ie primorials.
>
> For example the centerpoint 8 has 2 valid equations using primes for N:
> (11-5)/2=3
> (13-3)/2=5
>
> ie. here is the count of how many equations all the centerpoints from 0 to
> 216 have, and
> centerpoint 210 a primorial has the most equations.
>
> 0 0
> 1 0
> 2 0
> 3 0
> 4 0
> 5 1
> 6 0
> 7 0
> 8 2
> 9 1
> 10 2
> 11 0
> 12 2
> 13 0
> 14 1
> 15 1
> 16 2
> 17 0
> 18 3
> 19 0
> 20 2
> 21 1
> 22 1
> 23 0
> 24 5
> 25 0
> 26 1
> 27 0
> 28 0
> 29 0
> 30 5
> 31 0
> 32 1
> 33 0
> 34 1
> 35 0
> 36 5
> 37 0
> 38 0
> 39 1
> 40 1
> 41 0
> 42 6
> 43 0
> 44 1
> 45 1
> 46 1
> 47 0
> 48 5
> 49 0
> 50 2
> 51 0
> 52 0
> 53 0
> 54 5
> 55 0
> 56 2
> 57 0
> 58 0
> 59 0
> 60 10
> 61 0
> 62 0
> 63 0
> 64 1
> 65 0
> 66 8
> 67 0
> 68 0
> 69 1
> 70 2
> 71 0
> 72 6
> 73 0
> 74 0
> 75 0
> 76 2
> 77 0
> 78 8
> 79 0
> 80 0
> 81 1
> 82 0
> 83 0
> 84 10
> 85 0
> 86 1
> 87 0
> 88 0
> 89 0
> 90 12
> 91 0
> 92 1
> 93 0
> 94 0
> 95 0
> 96 7
> 97 0
> 98 0
> 99 1
> 100 2
> 101 0
> 102 7
> 103 0
> 104 1
> 105 1
> 106 1
> 107 0
> 108 7
> 109 0
> 110 1
> 111 1
> 112 0
> 113 0
> 114 8
> 115 0
> 116 1
> 117 0
> 118 0
> 119 0
> 120 16
> 121 0
> 122 0
> 123 0
> 124 0
> 125 0
> 126 11
> 127 0
> 128 0
> 129 1
> 130 1
> 131 0
> 132 8
> 133 0
> 134 1
> 135 0
> 136 0
> 137 0
> 138 6
> 139 0
> 140 1
> 141 0
> 142 1
> 143 0
> 144 12
> 145 0
> 146 0
> 147 0
> 148 0
> 149 0
> 150 13
> 151 0
> 152 0
> 153 0
> 154 1
> 155 0
> 156 10
> 157 0
> 158 0
> 159 0
> 160 2
> 161 0
> 162 11
> 163 0
> 164 0
> 165 1
> 166 0
> 167 0
> 168 13
> 169 0
> 170 2
> 171 0
> 172 0
> 173 0
> 174 10
> 175 0
> 176 2
> 177 0
> 178 0
> 179 0
> 180 16
> 181 0
> 182 0
> 183 0
> 184 0
> 185 0
> 186 13
> 187 0
> 188 0
> 189 0
> 190 0
> 191 0
> 192 6
> 193 0
> 194 1
> 195 1
> 196 2
> 197 0
> 198 9
> 199 0
> 200 1
> 201 0
> 202 1
> 203 0
> 204 12
> 205 0
> 206 0
> 207 0
> 208 0
> 209 0
> 210 26
> 211 0
> 212 0
> 213 0
> 214 0
> 215 0
> 216 9
>
>
> Here is a graph showing this too:
>
> zoomed in: (shows the primorial peaks)
> http://imgur.com/x7yDW1e
>
> zoomed out: (shows the primorial multiple bands forming)
> http://imgur.com/gcw7S39
>
>
> cheers,
> Jamie
>
>
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