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A335428 Prime exponent of the first Fermi-Dirac factor (number of form p^(2^k)), A050376) reached, when starting from n and iterating with A334870, with a(1) = 0. 2
0, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 4, 1, 2, 1, 2, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 4, 2, 2, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 4, 4, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 1, 1, 4, 1, 2, 2, 1, 1, 1, 1, 2, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

EXAMPLE

For n=27, when iterating with A334870, we obtain the path 27 -> 18 -> 9, with that 9 being the first prime power encountered that has an exponent of the form 2^k, as 9 = 3^2, thus a(27) = 2. See the binary tree A334860 or A334866 for how such paths go.

For n=900, when iterating with A334870 we obtain the path 900 -> 30 -> 15 -> 10 -> 5, and 5^1 is finally a prime power with an exponent that is two's power, thus a(900) = 1. Note that 900 is the first such position of 1 in this sequence that is not listed in A333634.

PROG

(PARI)

A209229(n) = (n && !bitand(n, n-1));

A302777(n) = A209229(isprimepower(n));

A334870(n) = if(issquare(n), sqrtint(n), my(c=core(n), m=n); forprime(p=2, , if(!(c % p), m/=p; break, m*=p)); (m));

A335428(n) = { while(n>1 && !A302777(n), n = A334870(n)); isprimepower(n); };

(PARI)

\\ Faster, A209229 and A302777 like in above:

A335428(n) = if(1==n, 0, while(!A302777(n), if(issquarefree(n), return(1)); if(issquare(n), n = sqrtint(n), n /= core(n))); isprimepower(n));

CROSSREFS

Cf. A050376, A209229, A302777, A334860, A334866, A334870, A334872.

Sequence in context: A299090 A046951 A159631 * A050377 A255231 A294874

Adjacent sequences:  A335425 A335426 A335427 * A335429 A335430 A335431

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jun 26 2020

STATUS

approved

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Last modified April 13 00:24 EDT 2021. Contains 342934 sequences. (Running on oeis4.)