A173966 Sums of two consecutive semiprimes.

19, 29, 43, 51, 67, 69, 77, 115, 171, 173, 187, 189, 237, 243, 245, 267, 283, 285, 291, 317, 355, 403, 405, 411, 427, 429, 435, 437, 507, 597, 603, 605, 653, 669, 723, 763, 787, 789, 891, 893, 907, 963, 1003, 1029, 1053, 1075, 1085, 1107, 1131, 1245, 1267

Offset

1,1

Comments

First 16 terms:19,29,43,51,67,69,77,115,171,173,187,189,237,243,245,267 are the same as in A157483.

These are sums of two consecutive integers which are both semiprimes, whereas A118717 are sums of two semiprimes which are adjacent (consecutive) in A001358. [From R. J. Mathar, Mar 18 2010]

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1, 1}||Last/@FactorInteger[n]=={2}; lst={}; Do[If[f[n], If[f[n+1], AppendTo[lst, 2*n+1]]], {n, 7!}]; lst
Total/@Select[Partition[Select[Range[700], PrimeOmega[#]==2&], 2, 1], #[[2]]- #[[1]] == 1&] (* Harvey P. Dale, Jun 22 2020 *)

Crossrefs

Sequence in context: A276049 A108183 A157483 * A096218 A100590 A046120

Adjacent sequences: A173963 A173964 A173965 * A173967 A173968 A173969

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Mar 03 2010

Status

approved