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A069563
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a(1) = 1, a(2) = 4; for n > 2, a(n) = k*a(n-1) + 1 where k is smallest number > 1 such that k*a(n-1) + 1 is a multiple of n.
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2
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1, 4, 9, 28, 85, 426, 3409, 23864, 167049, 1837540, 18375401, 128627808, 1157650273, 10418852458, 83350819665, 1250262294976, 22504721309569, 382580262262674, 4973543409414763, 64656064322391920, 99470868188295261
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| a(6) = 426, a(7) = 3409 since 3409 = 8*426 + 1 is a multiple of 7.
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MATHEMATICA
| a[1] = 1; a[n_] := a[n] = Module[{k}, If[ Intersection[ Transpose[ FactorInteger[a[n - 1]]] [[1]], Transpose[ FactorInteger[n]] [[1]]] == {}, k = 2; While[ !IntegerQ[(k*a[n - 1] + 1)/n], k++ ]; Return[ k*a[n - 1] + 1], k = 1; While[ !IntegerQ[(k*a[n - 2] + 1)/n], k++ ]; Return[ k*a[n - 2] + 1]]]; Table[ a[n], {n, 1, 23}]
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CROSSREFS
| Sequence in context: A000368 A094255 A192234 * A059345 A127768 A186650
Adjacent sequences: A069560 A069561 A069562 * A069564 A069565 A069566
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Mar 23 2002
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EXTENSIONS
| More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Mar 23 2002
Edited, corrected and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 12 2002
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