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 A212038 The size of the set of numbers k>=0 such that all (2^n-k)*2^n-1 are prime but only (2^n-k)*2^n+1 with the largest k is also the associated twin prime. 1
 1, 7, 5, 2, 4, 11, 6, 1, 3, 2, 31, 2, 11, 11, 11, 6, 30, 16, 2, 36, 90, 56, 11, 52, 13, 36, 10, 62, 20, 31, 23, 28, 30, 14, 47, 22, 10, 5, 104, 39, 11, 14, 64, 184, 209, 176, 193, 162, 25, 38, 23, 5, 27, 157, 5, 17, 32, 90, 1, 199, 96, 83, 29, 82, 12, 220, 19, 40, 37, 13, 16, 120, 11, 130, 12, 77, 202 (list; graph; refs; listen; history; text; internal format)
 OFFSET 4,2 COMMENTS Search set similar to A212037 but the sign of k in the prime form is switched. Heuristically the average of a(n)/n for n=1 to N tends to 1 as N increases. LINKS Pierre CAMI, Table of n, a(n) for n = 4..825 MAPLE A212038 := proc(n)     local a, k, p ;     a := 0 ;     for k from 0 do         p := (2^n-k)*2^n-1 ;         if isprime(p) then             a := a+1 ;         end if;         if isprime(p) and isprime(p+2) then             return a;         end if;     end do: end proc: # R. J. Mathar, Jul 21 2012 PROG SCRIPT DIM nn, 3 DIM jj DIM kk DIMS tt OPENFILEOUT myfile, a(n).txt LABEL loopn SET nn, nn+1 IF nn>825 THEN END SET kk, -1 SET jj, 0 LABEL loopk SET kk, kk+1 SETS tt, %d, %d\,; nn; kk PRP (2^nn-kk)*2^nn-1, tt IF ISPRP THEN GOTO a IF ISPRIME THEN GOTO a GOTO loopk LABEL a SET jj, jj+1 PRP (2^nn-kk)*2^nn+1, tt IF ISPRP THEN GOTO d IF ISPRIME THEN GOTO d GOTO loopk LABEL d SETS tt, %d, %d\,; nn; jj WRITE myfile, tt GOTO loopn CROSSREFS Cf. A191619, A191620, A205322. Sequence in context: A070404 A258370 A135537 * A335863 A112545 A021934 Adjacent sequences:  A212035 A212036 A212037 * A212039 A212040 A212041 KEYWORD nonn AUTHOR Pierre CAMI, Jul 14 2012 STATUS approved

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Last modified September 27 03:21 EDT 2020. Contains 337380 sequences. (Running on oeis4.)