A127118 a(n) = n-th prime * n-th nonprime.

2, 12, 30, 56, 99, 130, 204, 266, 345, 464, 558, 740, 861, 946, 1128, 1325, 1534, 1647, 1876, 2130, 2336, 2607, 2822, 3115, 3492, 3838, 4017, 4280, 4578, 4972, 5715, 6026, 6576, 6811, 7450, 7701, 8164, 8802, 9185, 9688, 10203, 10498, 11460, 11966, 12411

Offset: 1

Author

Neven Juric (neven.juric(AT)apis-it.hr), Mar 21 2007

Keywords

• nonn
• easy

Links

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

Crossrefs

Cf. A000040, A018252, A002808.

Cf. A014237, A064799, A067563.

Programs

Haskell

a127118 n = a000040 n * a018252 n  -- Reinhard Zumkeller, Apr 30 2014

Mathematica

Module[{nn=100,prs,non,len},prs=Prime[Range[nn]];non=Complement[ Range[ nn],prs]; len=Min[Length[prs],Length[non]]; Times@@#&/@ Thread[ {Take[ prs,len],Take[non,len]}]] (* Harvey P. Dale, Dec 29 2012 *)

Python

from sympy import prime, composite
def A127118(n):
    return 2 if n == 1 else prime(n)*composite(n-1) # Chai Wah Wu, Dec 27 2018

Formula

a(n) = A000040(n) * A018252(n).