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A091815
Numbers m such that the numerator of Sum_{i=1..m} (i-1)/i is prime.
2
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
1,1
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..93
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 *)
PROG
(PARI) ss(n)=sum(i=1, n, (i-1)/i); for (i=1, 1200, if(isprime(numerator(ss(i))), print1(i, ".")))
CROSSREFS
Sequence in context: A047564 A154536 A298110 * A081692 A161346 A096515
KEYWORD
hard,nonn
AUTHOR
Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 07 2004
EXTENSIONS
a(39)-a(46) from Harvey P. Dale, Jul 13 2011
a(47) and beyond from Michael S. Branicky, Aug 26 2024
STATUS
approved