7 Sep
2005
7 Sep
'05
8:21 a.m.
Wed, 7 Sep 2005 15:21:39 +0200 "Eric Angelini" <keynews.tv@skynet.be> Hello SeqFan, consider this array where the 1st column is made of all prime numbers, and the nth term of a row is 2 times the previous one on the same row [P(n)=P*2^n]: ... 1) The missing integers in this array are : 1 9 15 18 21 25 27 30 33 35 36 39 42 45 ... ...which (except the first term 1) are A093642. Actually, I think the def'n is the same as A105441, not A093642. A105441 is probably easier to compute directly than by building your array (trim off low order zeros in binary rep and see if result is prime or not).