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A152076
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a(n) = the largest prime p < p(n) such that p(n) - p is squarefree, where p(n) is the n-th prime. a(n) = 0 if no such prime p exists.
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3
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2, 3, 5, 5, 11, 11, 17, 17, 23, 29, 31, 31, 41, 41, 47, 53, 59, 61, 61, 71, 73, 73, 83, 83, 79, 101, 101, 107, 107, 113, 109, 131, 137, 139, 149, 151, 157, 157, 167, 173, 179, 181, 191, 191, 197, 197, 197, 197, 227, 227, 233, 239, 241, 251, 257, 263, 269, 271, 271
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| Does every odd prime differ from some smaller prime by a squarefree integer? Or is there at least one term of this sequence equal to 0?
Indices for which a(n)<a(n-1) are n = 26, 32, 64, 79, 89, 92, 98, 100, 123, 127, 129, 133, 136, 148, 152, 159, 164, 169, 181, 193,... [From M. F. Hasler (www.univ-ag.fr/~mhasler), Nov 23 2008]
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PROG
| (PARI) A152076(n) = { local(q=n=prime(n)); while( q=precprime(q-1), issquarefree(n-q) & return(q))} [From M. F. Hasler (www.univ-ag.fr/~mhasler), Nov 23 2008]
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CROSSREFS
| Cf. A152075, A152073.
Sequence in context: A066911 A071850 A092749 * A138181 A133278 A050368
Adjacent sequences: A152073 A152074 A152075 * A152077 A152078 A152079
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Nov 23 2008
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EXTENSIONS
| Terms beyond a(13) from M. F. Hasler (www.univ-ag.fr/~mhasler) and Ray Chandler (rayjchandler(AT)sbcglobal.net), Nov 23 2008
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