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A109805
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a(n) = prime(n+2)*prime(n+1) - prime(n)*prime(n+1).
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4
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9, 20, 42, 66, 78, 102, 114, 230, 232, 248, 370, 246, 258, 470, 636, 472, 488, 670, 426, 584, 790, 830, 1246, 1164, 606, 618, 642, 654, 2034, 2286, 1310, 1096, 1668, 1788, 1208, 1884, 1630, 1670, 2076, 1432, 2172, 2292, 1158, 1182, 2786, 5064, 3568, 1362
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OFFSET
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1,1
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COMMENTS
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9 is the only semiprime of the form prime(n+2)*prime(n+1) - prime(n)*prime(n+1).
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LINKS
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MATHEMATICA
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Table[Prime[n + 1]*(Prime[n + 2] - Prime[n]), {n, 48}] (* Ray Chandler, Aug 17 2005 *)
#[[2]](#[[3]]-#[[1]])&/@Partition[Prime[Range[50]], 3, 1] (* Harvey P. Dale, Apr 01 2018 *)
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PROG
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(Python)
from sympy import prime, primerange
def aupton(nn):
alst, prevp, prev_prod = [], 2, 6
for p in primerange(3, prime(nn+2)+1):
cur_prod = prevp * p
alst.append(cur_prod - prev_prod)
prevp = p
prev_prod = cur_prod
return alst[1:]
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CROSSREFS
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The largest prime factor of a(n) gives the sequence A065091.
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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