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A023583
Greatest prime divisor of 2*prime(n)-1.
1
3, 5, 3, 13, 7, 5, 11, 37, 5, 19, 61, 73, 3, 17, 31, 7, 13, 11, 19, 47, 29, 157, 11, 59, 193, 67, 41, 71, 31, 5, 23, 29, 13, 277, 11, 43, 313, 13, 37, 23, 17, 19, 127, 11, 131, 397, 421, 89, 151, 457, 31, 53, 37, 167, 19, 7, 179, 541, 79, 17, 113, 13, 613, 23, 5
OFFSET
1,1
COMMENTS
a(n) = 2*prime(n)-1 if n is in A137288. - Robert Israel, May 19 2020
LINKS
FORMULA
a(n) = A006530(A076274(n+1)). - Bernard Schott, May 20 2020
MAPLE
f:= n -> max(numtheory:-factorset(2*ithprime(n)-1)):
map(f, [$1..100]); # Robert Israel, May 19 2020
MATHEMATICA
a[n_] := FactorInteger[2*Prime[n]-1][[-1, 1]]; Array[a, 100] (* Amiram Eldar, Oct 27 2024 *)
PROG
(PARI) a(n) = {my(f = factor(2*prime(n)-1)); f[#f~, 1]; } \\ Amiram Eldar, Oct 27 2024
CROSSREFS
KEYWORD
nonn,easy
EXTENSIONS
Name edited by Robert Israel, May 19 2020
STATUS
approved