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A196558 a(n) is the index of the first occurrence of n in A195061. 0
2, 36, 108, 284 (list; graph; refs; listen; history; text; internal format)



In sequence A195061, element 2 through 25 are 1, which means it is possible to find a sum of p=b+c, p is the n-th prime number, the prime factors of b and c traverse all primes smaller than square root p(n). From element 36, the above case does no longer stand for most of primes. However, if you pick two eligible sum p=b1+c1=b2+c2, it becomes possible that the union set of prime factors of b1, c1, b2, and c2 traverse all primes smaller than square root p(n). This stands until p(107)=587. For p(108)=593, no group of two b and cs can have the union set of their prime factors to traverse all primes smaller than square root p(n).  Three groups of b and cs will be needed to do so. And starting from p(284)=1861, four groups are needed for some of the numbers.

The listed Mathematica program failed in finding a(5) since it exceeded the integer range as index.


Table of n, a(n) for n=1..4.


A195061[2]=1 => a(1)=2;

A195061[3]=A195061[4]=...=A195061[35]=1; A195061[36]=2 => a(2)=36;

A195061[1..107]<=2; A195061[108]=3 => a(3)=108;

A195061[1..283]<=3; A195061[284]=4 => a(4)=284;


(* Taking the function Checks[n_] in the Mathematica program for A195061, the following program gives the first four terms: *) k = 0; i = 1; a = 0; Array[ff, 4]; Do[ff[j] = 0, {j, 1, 4}]; While[(k < 4) && (a < 4), i++; a = Checks[i]; If[(a <= 4) && (ff[a] == 0), ff[a] = i; k++]]; Table[ff[m], {m, 4}]


Cf. A196526, A195061.

Sequence in context: A278930 A258356 A145450 * A187509 A134785 A143745

Adjacent sequences:  A196555 A196556 A196557 * A196559 A196560 A196561




Lei Zhou, Oct 03 2011



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Last modified January 24 04:47 EST 2022. Contains 350534 sequences. (Running on oeis4.)