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A133795 a(n) = n-th semiprime + n-th non-semiprime. 1
5, 8, 12, 15, 21, 23, 32, 34, 38, 42, 50, 52, 54, 58, 62, 70, 76, 79, 84, 87, 89, 94, 101, 106, 114, 118, 124, 128, 130, 132, 138, 141, 144, 147, 159, 165, 171, 177, 179, 182, 185, 187, 195, 200, 202, 211, 213, 215, 218, 221, 231, 236, 238, 241, 247, 252, 261 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Semiprime analog of A022797 n-th prime + n-th nonprime. a(n) is prime for n = 1, 6, 18, 21, 23. a(n) is itself semiprime for n = 4, 5, 22, 25, 38, 39, 57, 62, 69, 77 of which first 10 indices all but n=5 are themselves semiprimes.

LINKS

Table of n, a(n) for n=1..57.

FORMULA

a(n) = A001358(n) + A100959(n).

EXAMPLE

a(1) = 1st semiprime + 1st nonsemiprime = 4 + 1 = 5.

a(2) = 2nd semiprime + 2nd nonsemiprime = 6 + 2 = 8.

a(3) = 3rd semiprime + 3rd nonsemiprime = 9 + 3 = 12.

MAPLE

A100959 := proc(n) option remember; local a ; if n = 1 then 1 ; else for a from A100959(n-1)+1 do if numtheory[bigomega](a) <> 2 then RETURN(a) ; fi ; od: fi ; end: A001358 := proc(n) option remember ; local a ; if n = 1 then 4 ; else for a from A001358(n-1)+1 do if numtheory[bigomega](a) = 2 then RETURN(a) ; fi ; od: fi ; end: A133795 := proc(n) A100959(n)+A001358(n) ; end: seq(A133795(n), n=1..100) ; # R. J. Mathar, Jan 09 2008

CROSSREFS

Cf. A000040, A001358, A022797, A100959.

Sequence in context: A047383 A322534 A314402 * A247060 A314403 A314404

Adjacent sequences:  A133792 A133793 A133794 * A133796 A133797 A133798

KEYWORD

easy,nonn,less

AUTHOR

Jonathan Vos Post, Jan 05 2008

EXTENSIONS

Corrected and extended by R. J. Mathar, Jan 09 2008

STATUS

approved

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Last modified May 25 21:44 EDT 2022. Contains 354071 sequences. (Running on oeis4.)