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 2007-04-15, 05:53 #1 Citrix     Jun 2003 158510 Posts Smallest floor of k for cullen prime A related problem to the project. Find the smallest floor of k for a cullen prime? eg. 18496*2^18496+1 is prime and 18496=2^4*17^2. Hence 17 is the floor of the k for this prime. what is the smallest floor value, a Cullen prime can have? (1*2^1+1 does not count) Looking at 2^n*2^(2^n)+1 then n+2^n must be equal to 2^m (This is not possible) So what about k=2^x*3^y? I looked at values with floor<=13 and k=1.5M to 5M and sieved to p=2.5G Values left=96 Code: 1522521 2 +1 1542294 2 +1 1544400 2 +1 1548288 2 +1 1607445 2 +1 1660932 2 +1 1670625 2 +1 1702701 2 +1 1711125 2 +1 1774500 2 +1 1791153 2 +1 1835008 2 +1 1837500 2 +1 1848000 2 +1 1848015 2 +1 1976832 2 +1 1980825 2 +1 2027520 2 +1 2037420 2 +1 2047032 2 +1 2050048 2 +1 2076165 2 +1 2079000 2 +1 2096640 2 +1 2112000 2 +1 2167074 2 +1 2200000 2 +1 2207205 2 +1 2222640 2 +1 2258685 2 +1 2293200 2 +1 2321865 2 +1 2359296 2 +1 2371600 2 +1 2376990 2 +1 2396160 2 +1 2415765 2 +1 2416128 2 +1 2419200 2 +1 2469852 2 +1 2480625 2 +1 2578125 2 +1 2704000 2 +1 2772000 2 +1 2788500 2 +1 2810808 2 +1 2881200 2 +1 2889432 2 +1 2918916 2 +1 2940000 2 +1 2956800 2 +1 2976750 2 +1 2988216 2 +1 3000000 2 +1 3007125 2 +1 3080025 2 +1 3130218 2 +1 3243240 2 +1 3279276 2 +1 3281250 2 +1 3294225 2 +1 3294720 2 +1 3312400 2 +1 3369600 2 +1 3388000 2 +1 3430000 2 +1 3435432 2 +1 3440640 2 +1 3503500 2 +1 3592512 2 +1 3639168 2 +1 3649536 2 +1 3651921 2 +1 3704778 2 +1 3748096 2 +1 3773952 2 +1 3802500 2 +1 3893760 2 +1 3931200 2 +1 3936600 2 +1 3960000 2 +1 4009500 2 +1 4026880 2 +1 4077216 2 +1 4164160 2 +1 4198467 2 +1 4276800 2 +1 4392300 2 +1 4563000 2 +1 4658500 2 +1 4764375 2 +1 4791600 2 +1 4840000 2 +1 4851495 2 +1 4915625 2 +1 4919376 2 +1