OFFSET
1,1
COMMENTS
Composite numbers produced in A053176.
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
R. P. Boas & N. J. A. Sloane, Correspondence, 1974
FORMULA
From the composite, subtract 1, divide by 2 and result is a prime.
EXAMPLE
a(3)=35 and 35-1=34, 34/2=17, prime.
MATHEMATICA
Select[2 Prime@ Range@ 74 + 1, CompositeQ] (* Michael De Vlieger, Jul 13 2015 *)
Select[Range[1, 801, 2], CompositeQ[#]&&PrimeQ[(#-1)/2]&] (* Harvey P. Dale, Apr 01 2019 *)
PROG
(PARI) main(size)={my(v=vector(size), i, t=1); for(i=1, size, while(isprime(2*prime(t)+1), t++); v[i]=2*prime(t)+1; t++; ); return(v)} /* Anders Hellström, Jul 13 2015 */
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Enoch Haga, Feb 29 2000
EXTENSIONS
Definition clarified by Peter Munn, Oct 26 2017
STATUS
approved