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A181542 Numbers k such that there is at least one pair of twin primes 3^k - 3^j -+ 1 with k/2 <= j < k. 1
2, 3, 4, 11, 12, 18, 20, 30, 35, 47, 108, 113, 118, 127, 136, 162, 165, 212, 502, 656, 1131, 1560, 1620, 1966, 2293, 4184, 5568 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..27.

MAPLE

isA181542 := proc(n) local nh, k, p; if type(n, 'even') then nh := n/2; else nh := (n+1)/2; end if; for k from n-1 to nh by -1 do p := 3^n-3^k-1 ; if isprime(p) and isprime(p+2) then return true; end if; end do ; false; end proc:

for n from 1 do if isA181542(n) then print(n); end if; end do; # R. J. Mathar, Feb 05 2011

CROSSREFS

Cf. A181551, A181515, A181523.

Sequence in context: A268236 A039023 A110918 * A160914 A326377 A155768

Adjacent sequences:  A181539 A181540 A181541 * A181543 A181544 A181545

KEYWORD

nonn

AUTHOR

Pierre CAMI, Jan 29 2011, Feb 05 2011

STATUS

approved

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Last modified September 19 15:31 EDT 2019. Contains 327199 sequences. (Running on oeis4.)