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Search: id:A089188
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| A089188 |
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Lower member p of a pair of twin primes such that p-1 is squarefree. |
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+0
2
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| 3, 11, 59, 71, 107, 179, 191, 227, 239, 311, 347, 419, 431, 599, 659, 827, 1019, 1031, 1091, 1319, 1427, 1487, 1607, 1619, 1787, 1871, 1931, 2027, 2087, 2111, 2267, 2339, 2591, 2687, 2711, 2999, 3119, 3167, 3299, 3359, 3371, 3467, 3527, 3539, 3671, 3767
(list; graph; listen)
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OFFSET
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0,1
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EXAMPLE
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71 is included because 71-1 = 2*5*7. 17 is omitted because 17-1 = 2^4.
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PROGRAM
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(PARI) pm1th(n) = { c=0; pc=0; forprime(x=2, n, pc++; y=x-1; if(isprime(x+2), if(issquarefree(y), c++; print1(x", "); ) ) ); print(); print(c", "pc", "c/pc+.0) }
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CROSSREFS
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Sequence in context: A009444 A141776 A071698 this_sequence A086827 A164291 A137690
Adjacent sequences: A089185 A089186 A089187 this_sequence A089189 A089190 A089191
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Dec 07 2003
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