A Fortunate number, named after Reo Fortune, for a given positive integer n is the smallest integer m > 1 such that pn# + m is a prime number, where the primorial pn# is the product of the first n prime numbers.
For example, p7# = 2×3×5×7×11×13 = 510,510. The smallest prime number after 510,511 is 510,529. Thus, 510,529 - 510,510 = 29 is a Fortunate number.
Fortune's conjecture states that no Fortunate number is composite. A Fortunate prime is a Fortunate number which is also a prime number. As of 2009, all the known Fortunate numbers are also Fortunate primes.
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Instead of only using primorial numbers in our sequence, what happens when we use all numbers such that for the largest prime dividing each number in our sequence, the primorial of that prime also divides that number (i.e., 630 = 2×32×5×7 belongs to the sequence since p4# = 210 divides 630)?
512 → 25, 16,384 → 29, and 524,288 → 214 fail to generate Fortunate primes.
Do only perfect powers of two fail to generate Fortunate primes? Is there a pattern?
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For all numbers less than a billion in our sequence, the following fail to generate a Fortunate prime:
F# Generator
9 512
9 8,388,608
15 4,194,304
15 67,108,864
21 524,288
25 147,456
25 373,248
25 393,216
25 1,062,882
25 1,259,712
25 4,251,528
25 4,718,592
25 5,308,416
25 5,971,968
25 10,077,696
25 17,915,904
25 21,233,664
25 35,831,808
25 42,467,328
25 172,186,884
27 16,384
35 1,119,744
35 1,492,992
35 33,554,432
35 47,775,744
35 150,994,944
35 362,797,056
49 22,118,400
49 31,104,000
49 32,805,000
49 42,187,500
49 56,623,104
49 90,000,000
49 286,654,464
49 364,500,000
49 720,000,000
49 859,963,392
55 679,477,248
65 10,616,832
77 159,252,480
77 188,956,800
85 322,486,272
119 314,572,800
Thursday, November 05, 2009
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