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A267000 a(n) is the smallest m such that A001414(m)=n and ((m=0) mod n) and m/n is both squarefree and prime to n, or 0 if no such m exists. 0
2, 3, 4, 5, 0, 7, 0, 0, 30, 11, 60, 13, 70, 105, 240, 17, 0, 19, 220, 231, 0, 23, 0, 650, 286, 1755, 476, 29, 2730, 31, 1824, 627, 3570, 805, 4788, 37, 646, 897, 1160, 41, 8778, 43, 1276, 11385, 8970, 47, 1776, 36309, 10850, 1581, 41860, 53, 2322, 4070, 2408, 45885, 16530, 59 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

The offset is 2 like A056240 since there is no number m with A001414(m) = 1

Alladi and Erdős state that there is only a finite number of zeros in this sequence.

When a(n) is not zero, A056240(n) <= a(n); a(n) <= A000792(n).

LINKS

Table of n, a(n) for n=2..59.

K. Alladi and P. Erdős, On an additive arithmetic function, Pacific J. Math., Volume 71, Number 2 (1977), 275-294.

FORMULA

a(p) = p, for p prime.

EXAMPLE

a(10) = 30 since A001414(30)=10 and 30 is divisible by 10, and 30/10=3 is squarefree and prime to 10.

PROG

(PARI) sopfr(n) = {my(f=factor(n)); sum(k=1, #f~, f[k, 1]*f[k, 2]); }

first(n) = {my(k=1); while (sopfr(k) != n, k++); k; }

last(n) = polcoeff((1+x+2*x^2+x^4)/(1-3*x^3) + O(x^(n + 3)), n);

a(n) = {na = first(n); nb = last(n); for (m=na, nb, if ((sopfr(m) == n) && (! (m % n)) && issquarefree(m/n) && (gcd(m/n, n) == 1), return(m)); ); }

CROSSREFS

Cf. A000792, A001414, A036844, A056240, A064364.

Sequence in context: A195829 A095874 A279385 * A224892 A265517 A063972

Adjacent sequences:  A266997 A266998 A266999 * A267001 A267002 A267003

KEYWORD

nonn

AUTHOR

Michel Marcus, Jan 08 2016

STATUS

approved

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Last modified December 10 04:15 EST 2019. Contains 329885 sequences. (Running on oeis4.)