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A258091
Smallest prime factor of 1+78557*2^n, cf. A258073.
5
5, 3, 73, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 19, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 37, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 71, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 19, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 37, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 73, 3, 5, 3, 7, 3, 5, 3
OFFSET
1,1
COMMENTS
a(n) = A020639(A258073(a(n)));
a(n) <= 73; see also A258095.
Periodic, a(n) = a(n + 840420) for all n (and 840420 is minimal with this property). The only values that occur, are {3, 5, 7, 13, 19, 37, 73} union {47, 59, 71}. - Jeppe Stig Nielsen, Jul 19 2020
LINKS
PROG
(Haskell) a258091 = a020639 . a258073
(PARI) a(n)=forprime(p=2, , 78557*Mod(2, p)^n+1==0 && return(p)) \\ Jeppe Stig Nielsen, Jul 19 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Reinhard Zumkeller, May 19 2015
STATUS
approved