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A121315 Products of two consecutive prime powers. 1
2, 6, 12, 20, 35, 56, 72, 99, 143, 208, 272, 323, 437, 575, 675, 783, 899, 992, 1184, 1517, 1763, 2021, 2303, 2597, 3127, 3599, 3904, 4288, 4757, 5183, 5767, 6399, 6723, 7387, 8633, 9797, 10403, 11021, 11663, 12317, 13673, 15125, 15875, 16256, 16768 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For some algorithms for finding A034699(n), the numbers in this sequence represent a worst-case scenario of execution time.
LINKS
FORMULA
a(n) = A000961(n)*A000961(n+1).
EXAMPLE
437 = 19*23 and none of the intervening integers (20,21,22) are prime powers.
MATHEMATICA
t = Join[{1}, Select[Range[2, 131], Mod[ #, # - EulerPhi[ # ]] == 0 &]]; Most@t*Rest@t (* Robert G. Wilson v, Sep 02 2006 *)
PROG
(PARI) lista(nn) = v = concat(1, select(x->isprimepower(x), vector(nn, n, n))); for (n=1, #v-1, print1(v[n]*v[n+1], ", ")); \\ Michel Marcus, Mar 20 2015
CROSSREFS
Sequence in context: A184432 A003274 A259470 * A078878 A095361 A095362
KEYWORD
nonn
AUTHOR
Paul Richards, Aug 28 2006
EXTENSIONS
More terms from Robert G. Wilson v, Sep 02 2006
STATUS
approved

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Last modified March 29 03:41 EDT 2024. Contains 371264 sequences. (Running on oeis4.)