OFFSET
1,1
MAPLE
isA181542 := proc(n) local nh, k, p; if type(n, 'even') then nh := n/2; else nh := (n+1)/2; end if; for k from n-1 to nh by -1 do p := 3^n-3^k-1 ; if isprime(p) and isprime(p+2) then return true; end if; end do ; false; end proc:
for n from 1 do if isA181542(n) then print(n); end if; end do; # R. J. Mathar, Feb 05 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Jan 29 2011, Feb 05 2011
STATUS
approved