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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.
0
4, 12, 60, 180, 1620, 9720, 417960, 7523280, 308454480, 25293267360, 1593475843680, 74893364652960, 4793175337789440, 517662936481259520, 21224180395731640320, 4075042635980474941440, 611256395397071241216000
OFFSET
1,1
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
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Jun 09 2003
EXTENSIONS
Edited and extended by Robert G. Wilson v, Jun 15 2003
STATUS
approved