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 A138290 Numbers n such that 2^(n+1)-2^k-1 is composite for all 0 <= k < n. 4
 6, 14, 22, 26, 30, 36, 38, 42, 54, 57, 62, 70, 78, 81, 90, 94, 110, 122, 126, 132, 134, 138, 142, 147, 150, 158, 166, 168, 171, 172, 174, 178, 182, 190, 194, 198, 206, 210, 222, 238, 254, 285, 294, 312, 315, 318, 334, 336, 350, 366, 372, 382, 405, 414, 416, 432 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The binary representation of 2^(n+1)-2^k-1 has n 1-bits and one 0-bit. Note that prime n are very rare: 577 is the first and 5569 is the second. A208083(a(n)) = 0 (cf. A081118). [Reinhard Zumkeller, Feb 23 2012] LINKS T. D. Noe, Table of n, a(n) for n=1..275 FORMULA For these n, A095058(n)=0 and A110700(n)>1. EXAMPLE 6 is here because 95, 111, 119, 123, 125 and 126 are all composite. MATHEMATICA t={}; Do[num=2^(n+1)-1; k=0; While[k

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Last modified April 8 04:26 EDT 2020. Contains 333312 sequences. (Running on oeis4.)