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A097975
a(n) is the prime divisor of n which is >= sqrt(n), or 0 if there is no such prime divisor.
2
0, 2, 3, 2, 5, 3, 7, 0, 3, 5, 11, 0, 13, 7, 5, 0, 17, 0, 19, 5, 7, 11, 23, 0, 5, 13, 0, 7, 29, 0, 31, 0, 11, 17, 7, 0, 37, 19, 13, 0, 41, 7, 43, 11, 0, 23, 47, 0, 7, 0, 17, 13, 53, 0, 11, 0, 19, 29, 59, 0, 61, 31, 0, 0, 13, 11, 67, 17, 23, 0, 71, 0, 73, 37, 0, 19, 11, 13, 79, 0, 0, 41, 83
OFFSET
1,2
COMMENTS
Sequence also is the sum of distinct prime divisors of n which are >= sqrt(n). At most one prime divisor of n is >= square root of n.
MATHEMATICA
Do[l = Select[Select[Divisors[n], PrimeQ], # >= Sqrt[n]&]; If[Length[l] == 0, Print[0], Print[l[[1]]]], {n, 1, 50}] (* Ryan Propper, Jul 24 2005 *)
Array[Select[FactorInteger[#][[All, 1]], Function[p, p >= Sqrt@ #]] /. {{} -> {0}, {1} -> {0}} &, 83][[All, 1]] (* Michael De Vlieger, Dec 22 2017 *)
PROG
(PARI) a(n) = sumdiv(n, d, if (isprime(d) && (d^2 >= n), d)); \\ Michel Marcus, Dec 23 2017
CROSSREFS
Cf. A097974.
Sequence in context: A323021 A026235 A086281 * A130088 A369033 A078834
KEYWORD
nonn
AUTHOR
Leroy Quet, Sep 07 2004
EXTENSIONS
More terms from Ryan Propper, Jul 24 2005
More terms from Stefan Steinerberger, Jan 21 2006
Further terms from Diana L. Mecum, Jun 15 2007
STATUS
approved