login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A090530 Least multiple k of prime(n) such that (k-1,k+1) forms a twin prime pair, or 0 if no such number exists. 3
4, 6, 30, 42, 198, 312, 102, 228, 138, 348, 1302, 1998, 1230, 1032, 282, 6360, 1062, 15738, 1608, 1278, 6132, 10428, 4482, 4272, 11058, 4242, 618, 642, 5232, 2712, 18288, 3930, 822, 1668, 1788, 11778, 3768, 5868, 5010, 9342, 23628, 3258, 17190 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(n) is a multiple of 6*prime(n) for n>2. Conjecture: No term is zero.
LINKS
EXAMPLE
a(5) = 198 = 11*18, (197,199) forms a twin prime pair.
MATHEMATICA
For[n = 1, n < 40, n++, a := Prime[n]; k := 2; While[Not[PrimeQ[k*a + 1] && PrimeQ[k*a - 1]], k += 2]; Print[k*a]] (* Stefan Steinerberger, Feb 17 2006 *)
PROG
(PARI) a(n) = { my(k = 2, p = prime(n)); while (! (isprime(k*p-1) && isprime(k*p+1)), k++); k*p; } \\ Michel Marcus, Nov 12 2017
CROSSREFS
Cf. A014574, A090531, A294731 [a(n)/(6*prime(n))].
Sequence in context: A364737 A056221 A046849 * A154667 A093121 A248048
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Dec 07 2003
EXTENSIONS
More terms from David Wasserman, Dec 21 2005
More terms from Stefan Steinerberger, Feb 17 2006
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 2 23:50 EST 2024. Contains 370499 sequences. (Running on oeis4.)