A091815 Numbers m such that the numerator of Sum_{i=1..m} (i-1)/i is prime.
3, 4, 5, 6, 7, 9, 11, 13, 15, 16, 17, 22, 61, 69, 73, 97, 120, 125, 138, 141, 158, 180, 183, 220, 224, 317, 370, 457, 517, 546, 573, 648, 678, 692, 699, 804, 848, 1182, 1213, 1225, 1300, 1866, 2093, 2344, 2411, 2837, 3421, 4888, 5685, 6530, 6788, 7009, 7076, 7465, 7674, 7757
Offset: 1
Links
- Michael S. Branicky, Table of n, a(n) for n = 1..93
Programs
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Mathematica
Select[Range[3000],PrimeQ[Numerator[Sum[(i-1)/i,{i,#}]]]&] (* Harvey P. Dale, Jul 13 2011 *) Position[Accumulate[Table[(k-1)/k,{k,3000}]],?(PrimeQ[Numerator[#]]&)]// Flatten (* _Harvey P. Dale, Jun 06 2021 *) -
PARI
ss(n)=sum(i=1,n,(i-1)/i); for (i=1,1200,if(isprime(numerator(ss(i))),print1(i,".")))
Extensions
a(39)-a(46) from Harvey P. Dale, Jul 13 2011
a(47) and beyond from Michael S. Branicky, Aug 26 2024