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A100549 Let n = 2^e_2 * 3^e_ * 5^e_ * ... be the prime factorization of n; then a(n) = largest prime <= 1 + max{e_2, e_3, e_5, ...}; a(1) = 1 by convention. 6
1, 2, 2, 3, 2, 2, 2, 3, 3, 2, 2, 3, 2, 2, 2, 5, 2, 3, 2, 3, 2, 2, 2, 3, 3, 2, 3, 3, 2, 2, 2, 5, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 2, 5, 3, 3, 2, 3, 2, 3, 2, 3, 2, 2, 2, 3, 2, 2, 3, 7, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 3, 3, 2, 2, 2, 5, 5, 2, 2, 3, 2, 2, 2, 3, 2, 3, 2, 3, 2, 2, 2, 5, 2, 3, 3, 3, 2, 2, 2, 3, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

David Applegate and N. J. A. Sloane, Table of n, a(n) for n = 1..10000

EXAMPLE

If n = 8 = 2^3, a(n) = (largest prime <= 3+1) = 3.

If n = 480 = 2^5*3*5, a(n) = (largest prime <= 1 + max{5,1,1}) = 5.

MAPLE

# if n = prod_p p^e_p, then

# pp = largest prime <= 1 + max e_p

with(numtheory):

pp := proc(n) local f, m; option remember;

if (n = 1) then

return 1;

end if;

m := 1:

for f in op(2..-1, ifactors(n)) do

if (f[2] > m) then

m := f[2]:

end if;

end do;

prevprime(m+2);

end proc;

MATHEMATICA

{1}~Join~Array[Prime@PrimePi[1 + Max@FactorInteger[#][[All, -1]]] &, 105, 2] (* Michael De Vlieger, Nov 13 2018 *)

PROG

(PARI) a(n) = if (n==1, 1, precprime(1 + vecmax(factor(n)[, 2]~))); \\ Michel Marcus, Nov 14 2018

CROSSREFS

Cf. A100762, A100417, A141586, A082725.

Sequence in context: A278744 A082091 A334216 * A085962 A160821 A300225

Adjacent sequences:  A100546 A100547 A100548 * A100550 A100551 A100552

KEYWORD

nonn

AUTHOR

David Applegate and N. J. A. Sloane, Sep 15 2008

STATUS

approved

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Last modified July 2 09:21 EDT 2020. Contains 335398 sequences. (Running on oeis4.)