# [seqfan] Re: A175723: Why not monotonic and why repetitions?

Klaus Brockhaus klaus-brockhaus at t-online.de
Wed Aug 18 20:37:36 CEST 2010

```Multiples of 6 without surrounding twin primes.
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[ n: n in [6..600 by 6] | not IsPrime(n-1) or not IsPrime(n+1) ];

Magma V2.16-10    Thu Aug 19 2010 04:23:10    [Seed = 3657019619]
-------------------------------------

[ 24, 36, 48, 54, 66, 78, 84, 90, 96, 114, 120, 126, 132, 144, 156, 162,
168,
174, 186, 204, 210, 216, 222, 234, 246, 252, 258, 264, 276, 288, 294,
300, 306,
318, 324, 330, 336, 342, 354, 360, 366, 372, 378, 384, 390, 396, 402,
408, 414,
426, 438, 444, 450, 456, 468, 474, 480, 486, 492, 498, 504, 510, 516,
528, 534,
540, 546, 552, 558, 564, 576, 582, 588, 594 ]

Total time: 0.290 seconds, Total memory usage: 8.00MB
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? forstep(n=6,600,6,if(!(isprime(n-1)&&isprime(n+1)),print1(n,",")))
24,36,48,54,66,78,84,90,96,114,120,126,132,144,156,162,168,
174,186,204,210,216,222,234,246,252,258,264,276,288,294,300,306,
318,324,330,336,342,354,360,366,372,378,384,390,396,402,408,414,
426,438,444,450,456,468,474,480,486,492,498,504,510,516,528,534,
540,546,552,558,564,576,582,588,594,
time = [1;32m0 ms[0m.
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zak seidov schrieb:
> %S A175723 24,36,36,48,54,66,78,90,120,144,144,168,84,96,120,132,186
>
> %N A175723 These are multiples of 6 without surrounding twin primes.
>
> %C A175723 Why not monotonic and why repetitions?
>
> Zak
>

```