A078884 - OEIS

A078884

Greater member p of a twin prime pair such that p-1 is 3-smooth.

5, 7, 13, 19, 73, 109, 193, 433, 1153, 2593, 139969, 472393, 786433, 995329, 57395629, 63700993, 169869313, 4076863489, 10871635969, 2348273369089, 56358560858113, 79164837199873, 84537841287169, 150289495621633

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OFFSET

1,1

LINKS

Ray Chandler, Table of n, a(n) for n = 1..62 (terms < 10^1000, first 56 terms from Robert Israel)

FORMULA

a(n) = A027856(n) + 1 = A078883(n) + 2.

EXAMPLE

A000040(21)=73 and 73-1=72=2^3*3^2=A003586(17) and 73-2=71=A000040(20), therefore 73 is a term.

MAPLE

N:= 10^100:

sort(select(t -> isprime(t) and isprime(t-2),

[seq(seq(1+2^i*3^j, i=1..ilog2(floor(N/3^j))), j=0..floor(log[3](N)))])); # Robert Israel, May 14 2018

MATHEMATICA

1 + Select[With[{n = 10^15}, Sort@ Flatten@ Table[2^p * 3^q, {p, 0, Log2@ n}, {q, 0, Log[3, n/(2^p)]}] ], AllTrue[# + {-1, 1}, PrimeQ] &] (* Michael De Vlieger, May 14 2018 *)

CROSSREFS

Cf. A006512, A014574, A003586, A027856.

Essentially the same as A060211.

Sequence in context: A129782 A080829 A224789 * A314328 A314329 A154872

Adjacent sequences: A078881 A078882 A078883 * A078885 A078886 A078887

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 11 2002

STATUS

approved