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A343557
Indices of the prime factors of Fermat numbers in the sequence of primes.
1
2, 3, 7, 55, 116, 6543, 10847, 23974, 27567, 76709, 177975, 457523, 887643, 1625567, 2751966, 3772007, 9385401, 42401669, 61136051, 301137372, 2946723445, 7632981296, 24728168164, 98261951745, 99582868271, 159657063059, 231641062432, 851793186025, 870658222248
OFFSET
1,1
FORMULA
a(n) = A000720(A023394(n)).
A000040(a(n)) = A023394(n).
EXAMPLE
A000040(a(5)) = A000040(116) = 641 = A023394(5).
MAPLE
q:=n->(irem(2^(2^padic:-ordp(ithprime(n)-1, 2))-1, ithprime(n)) = 0):
select(q, [$1..10^5])[]; # Lorenzo Sauras Altuzarra, Feb 20 2023
PROG
(PARI) is_a023394(p)=p>2 && Mod(2, p)^lift(Mod(2, znorder(Mod(2, p)))^p)==1 && isprime(p) \\ after Charles R Greathouse IV in A023394
my(i=1); forprime(p=1, , if(is_a023394(p), print1(i, ", ")); i++) \\ Felix Fröhlich, Apr 30 2021
CROSSREFS
Cf. A000040 (primes), A000720 (primepi), A023394 (prime factors of Fermat primes).
Supersequence of A159611.
Sequence in context: A271041 A270402 A253574 * A238399 A159611 A156585
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Michel Marcus, Apr 29 2021
More terms from Amiram Eldar, Apr 29 2021
STATUS
approved