A305676 a(n) = A305671(A305672(n)).

7, 24, 72, 144, 240, 336, 504, 720, 576, 720, 1440, 2016, 2880, 4320, 5760, 10080, 10080, 10080, 10080, 8640, 8640, 10080, 17280, 15120, 17280, 17280, 17280, 20160, 30240, 40320, 60480, 120960, 181440, 241920, 362880, 483840, 725760, 1451520, 2177280, 2419200, 2419200

Offset

1,1

Comments

Do any numbers x exist that never occur in this sequence? Can this be proven for any particular value of x? For example, does 96 occur in this sequence? Note that 96 occurs four times as a value of sigma among the initial 100 composites.

Links

Table of n, a(n) for n=1..41.

Prog

(PARI) composite(n) = my(i=0); forcomposite(c=1, , i++; if(i==n, return(c)))
mcv(v) = my(w=vecsort(v, , 8), count=vector(#w), ind=0, i=0); for(x=1, #w, for(y=1, #v, if(w[x]==v[y], count[x]++))); for(k=1, #count, if(count[k]==vecmax(count), ind=k; i++)); if(i > 1, return(0), return(w[ind]))
a305671(n) = my(v=[]); for(k=1, n, v=concat(v, sigma(composite(k)))); mcv(v)
terms(n) = my(x=0, k=1, i=0); while(1, if(a305671(k) > 0, print1(a305671(k), ", "); i++); if(i==n, break); while(a305671(k) > 0, k++); while(a305671(k)==0, k++))
terms(11) \\ Print initial 11 terms of the sequence

Crossrefs

Cf. A145899, A305671, A305672, A305673, A305675, A305676.

Sequence in context: A217746 A211381 A339254 * A101903 A212504 A196349

Adjacent sequences: A305673 A305674 A305675 * A305677 A305678 A305679

Keyword

nonn

Author

Felix Fröhlich, Jun 08 2018

Status

approved