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A067605 Least k such that gcd(prime(k+1)-1, prime(k)-1) = 2n. 3
2, 6, 11, 24, 42, 121, 30, 319, 99, 1592, 344, 574, 3786, 4196, 650, 4619, 217, 1532, 11244, 5349, 8081, 3861, 12751, 18281, 9221, 5995, 22467, 16222, 43969, 35975, 192603, 108146, 52313, 218234, 15927, 132997, 42673, 78858, 103865, 84483 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Since all consecutive primes, p < q and p greater than 2, are odd, therefore gcd(p-1, q-1) must be even.

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

n=4: a(4) = 24 = gcd(89-1, 97-1) = gcd(p(24)-1, p(25)-1) = 8 = 2n.

MATHEMATICA

a = Table[0, {100}]; p = 3; q = 5; Do[q = Prime[n + 1]; d = GCD[p - 1, q - 1]/2; If[d < 101 && a[[d]] == 0, a[[d]] = n]; b = c, {n, 2, 10^7}]; a

CROSSREFS

Cf. A063444, A084307, A058263.

Sequence in context: A103143 A005673 A084308 * A072986 A079047 A160966

Adjacent sequences:  A067602 A067603 A067604 * A067606 A067607 A067608

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Jan 31 2002

STATUS

approved

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Last modified May 18 22:45 EDT 2021. Contains 344005 sequences. (Running on oeis4.)