A324384 - OEIS

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A324384

a(n) = gcd(n, A276154(n)), where A276154 is the primorial base left shift.

0, 1, 2, 1, 4, 1, 6, 1, 4, 1, 2, 11, 12, 1, 2, 1, 8, 1, 18, 1, 4, 7, 2, 1, 24, 1, 2, 1, 4, 1, 30, 1, 8, 1, 2, 7, 12, 1, 2, 1, 4, 1, 6, 1, 4, 1, 2, 1, 12, 1, 2, 1, 52, 1, 6, 1, 56, 1, 2, 1, 60, 1, 2, 1, 16, 1, 6, 1, 4, 1, 14, 1, 24, 1, 2, 1, 4, 1, 6, 1, 4, 1, 2, 1, 12, 1, 2, 1, 8, 1, 90, 1, 4, 1, 2, 1, 12, 1, 2, 1, 4, 1, 6, 1, 8, 1

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OFFSET

0,3

COMMENTS

For a very few primes, a(p) > 1 (then by necessity a(p) = p). In range 2 .. 2^25 there are three: 2, 11, 119039.

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..65537

Index entries for sequences related to primorial base

FORMULA

a(n) = gcd(n, A276154(n)).

PROG

(PARI)

A276151(n) = { my(s=1); forprime(p=2, , if(n%p, return(n-s), s *= p)); };

A276152(n) = { my(s=1); forprime(p=2, , if(n%p, return(s*p), s *= p)); };

A276154(n) = if(!n, n, (A276152(n) + A276154(A276151(n))));

\\ Alternatively, A276154 can be defined with A276085, A276086 and A003961:

A002110(n) = prod(i=1, n, prime(i));

A003961(n) = my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); \\ From A003961

A276085(n) = { my(f = factor(n)); sum(k=1, #f~, f[k, 2]*A002110(primepi(f[k, 1])-1)); };

A276086(n) = { my(i=0, m=1, pr=1, nextpr); while((n>0), i=i+1; nextpr = prime(i)*pr; if((n%nextpr), m*=(prime(i)^((n%nextpr)/pr)); n-=(n%nextpr)); pr=nextpr); m; };

A276154(n) = A276085(A003961(A276086(n)));

A324384(n) = gcd(n, A276154(n));

CROSSREFS

Cf. A002110, A049345, A276085, A276086, A276151, A276152, A276154, A323879, A324198, A324350, A324351.

Sequence in context: A128707 A257022 A214721 * A340081 A346467 A329641

Adjacent sequences: A324381 A324382 A324383 * A324385 A324386 A324387

KEYWORD

nonn

AUTHOR

Antti Karttunen, Feb 26 2019

STATUS

approved