OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
FORMULA
EXAMPLE
a(1)=1. a(2)=3+5+7+9=24. a(3)=5+7+9+11+13+15=60.
MAPLE
A014076 := proc(n) option remember; local a; if n = 1 then 1; else for a from procname(n-1)+2 by 2 do if not isprime(a) then RETURN(a) ; fi; od: fi; end:
A163636 := proc(n) local onpr; onpr := A014076(n) ; (onpr+2*n-1)*(onpr-2*n+3)/4; end: seq(A163636(n), n=1..80) ; # R. J. Mathar, Aug 08 2009
MATHEMATICA
A014076 := Select[Range[1, 10299, 2], PrimeOmega[#] != 1 &]; Table[(A014076[[n]] + 2*n - 1)*(A014076[[n]] - 2*n + 3)/4, {n, 1, 50}] (* G. C. Greubel, Jul 31 2017 *)
Module[{nn=201, onp}, onp=Select[Range[1, nn, 2], !PrimeQ[#]&]; Table[Total[ Range[ 2n-1, onp[[n]], 2]], {n, Length[onp]}]] (* Harvey P. Dale, Jul 03 2020 *)
PROG
(Python)
from sympy import primepi
def A163636(n):
if n == 1: return 1
m, k, n2 = n-1, primepi(n) + n - 1 + (n>>1), (n<<1)-1
while m != k:
m, k = k, primepi(k) + n - 1 + (k>>1)
return (lambda x: (x+n2)*(x-n2+2)>>2)(m) # Chai Wah Wu, Jul 31 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Aug 02 2009
EXTENSIONS
Edited and a(21) corrected by R. J. Mathar, Aug 08 2009
STATUS
approved