A104485 Primes p = p(k) such that prime(k) + 2 and prime(k+1) + 2 are both semiprimes.

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

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

19 is a term because prime(8) + 2 = 19 + 2 = 21 = 3*7 and prime(9) + 2 = 25 = 5*5.

Mathematica

fQ[n_] := Plus @@ Flatten[ Table[ #[[2]], {1}] & /@ FactorInteger[n]] == 2; Prime /@ Select[ Range[ 270], fQ[ Prime[ # ] + 2] && fQ[ Prime[ # + 1] + 2] &] (* Robert G. Wilson v, Apr 19 2005 *)
Select[Prime[Range[250]], PrimeOmega[#+2]==PrimeOmega[NextPrime[#]+2]==2&] (* Harvey P. Dale, Apr 01 2024 *)

Crossrefs

Cf. A063637.

Sequence in context: A104006 A117065 A006035 * A276569 A276447 A214796

Adjacent sequences: A104482 A104483 A104484 * A104486 A104487 A104488

Keyword

easy,nonn

Author

Giovanni Teofilatto, Apr 19 2005

Extensions

Corrected and extended by Robert G. Wilson v, Apr 19 2005

Status

approved