The On-Line Encyclopedia of Integer Sequences (OEIS)

A123093 revision #3

A123093

Numbers which are not the sum of two 3-almost primes.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 21, 22, 23, 25, 27, 29, 31, 33, 34, 37, 41, 43, 44, 49, 51, 59, 61, 66, 67, 85, 99, 101, 109, 163

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OFFSET

1,2

COMMENTS

3-almost prime analogue of A072966, numbers which are not the sum of two semiprimes. In general, it seems that almost all even numbers can be written as the sum of two k-almost primes for any positive integer k. - T. D. Noe (noe(AT)sspectra.com), Nov 06 2006

LINKS

Table of n, a(n) for n=1..42.

FORMULA

Complement of Sumset {A014612} + {A014612}.

MATHEMATICA

nn=10000; t3=Select[Range[2, nn], Plus@@Last/@FactorInteger[ # ]==3&]; t3sum=Table[0, {nn}]; Do[n=t3[[i]]+t3[[j]]; If[n<=nn, t3sum[[n]]=1], {i, Length[t3]}, {j, i, Length[t3]}]; Flatten[Position[t3sum, 0]] - T. D. Noe (noe(AT)sspectra.com), Nov 06 2006

CROSSREFS

Cf. A014612.

Sequence in context: A337379 A121684 A191853 * A191932 A044920 A330938

Adjacent sequences: A123090 A123091 A123092 * A123094 A123095 A123096

KEYWORD

easy,fini,full,nonn

AUTHOR

Jonathan Vos Post (jvospost3(AT)gmail.com), Sep 27 2006

EXTENSIONS

Edited by T. D. Noe (noe(AT)sspectra.com), Nov 06 2006

STATUS

approved