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Search: id:A104485
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| A104485 |
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Primes p = p(k) such that prime(k) + 2 and prime(k+1) + 2 are both semiprimes. |
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+0
1
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| 19, 31, 47, 83, 109, 113, 127, 199, 251, 257, 293, 353, 401, 443, 467, 479, 487, 491, 499, 503, 557, 571, 577, 647, 677, 743, 761, 787, 829, 863, 911, 937, 941, 947, 971, 977, 983, 1109, 1187, 1193, 1291, 1327, 1361, 1381, 1399, 1459, 1499, 1553, 1559
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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19 is a term because prime(8)+2=19+2=21=3*7 and prime(9)+2=25=5*5.
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MATHEMATICA
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fQ[n_] := Plus @@ Flatten[ Table[ #[[2]], {1}] & /@ FactorInteger[n]] == 2; Prime /@ Select[ Range[ 270], fQ[ Prime[ # ] + 2] && fQ[ Prime[ # + 1] + 2] &] (from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 19 2005)
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CROSSREFS
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Cf. A063637.
Sequence in context: A104006 A117065 A006035 this_sequence A141184 A033212 A104227
Adjacent sequences: A104482 A104483 A104484 this_sequence A104486 A104487 A104488
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KEYWORD
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easy,nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Apr 19 2005
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EXTENSIONS
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Corrected and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 19 2005
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