A084709 a(1) = 4, for n > 1, a(n) = smallest multiple of a(n-1) such that a(n)-1 and a(n)+1 are twin primes.

4, 12, 60, 180, 1620, 9720, 417960, 7523280, 308454480, 25293267360, 1593475843680, 74893364652960, 4793175337789440, 517662936481259520, 21224180395731640320, 4075042635980474941440, 611256395397071241216000

Offset

1,1

Links

Table of n, a(n) for n=1..17.

Mathematica

a[1] = 4; a[n_] := a[n] = Block[{k = 2}, While[ !PrimeQ[ k*a[n - 1] - 1] || !PrimeQ[ k*a[n - 1] + 1], k++ ]; k*a[n - 1]]; Table[ a[n], {n, 1, 17}]

Crossrefs

Sequence in context: A068525 A067755 A051858 * A057394 A054719 A356662

Adjacent sequences: A084706 A084707 A084708 * A084710 A084711 A084712

Keyword

nonn

Author

Amarnath Murthy, Jun 09 2003

Extensions

Edited and extended by Robert G. Wilson v, Jun 15 2003

Status

approved