OFFSET
1,1
COMMENTS
LINKS
Abhiram R Devesh, Table of n, a(n) for n = 1..48
Chris Caldwell,Cunningham Chain
EXAMPLE
a(1) = 41887255409, with associated Cunningham chain of length 5: 41887255409, 83774510819, 167549021639, 335098043279, 670196086559, each of which is the smaller of a pair of twin primes.
PROG
(Python)
p1=2
n=4
mx=10
count=0
while p1>2:
....## Generate the a chain of numbers with length 4
....cc=[]
....cc.append(p1)
....for i in range(1, n):
........cc.append((2**(i)*p1+((2**i)-1)))
....## chain entries + 2
....cc2=[c+2 for c in cc]
....## check if cc is a Cunningham Chain
....## pf.isp_list returns True or false for a given list of numbers
....## if they are prime or not
....##
....pcc=pf.isp_list(cc)
....pcc2=pf.isp_list(cc2)
....## Number of primes for cc
....npcc=pcc.count(True)
....## Number of primes for cc2
....npcc2=pcc2.count(True)
....if npcc==n and npcc2==n:
........print "For length ", n, " the series is : ", cc, " and ", cc2
....p1=pf.nextp(p1)
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Abhiram R Devesh, Feb 08 2014
STATUS
approved