login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

a(n) is the smallest integer k > 1 such that k cannot be expressed as a sum of distinct earlier terms nor is a multiple of any earlier term.
3

%I #30 Dec 02 2019 11:24:27

%S 2,3,7,11,17,25,59,67,185,193,563,571,1697,1747,5141,5149,11995,25727,

%T 27439,78893,82345,240131,243583,723845,727297,2174987,2178439,

%U 6530119,6530123,13061947,19590377,39182441,52242689,91425127,195910507,235092943,626913953

%N a(n) is the smallest integer k > 1 such that k cannot be expressed as a sum of distinct earlier terms nor is a multiple of any earlier term.

%C Conjecture: Composite terms k greater than 25 will have either two or six nontrivial divisors (that is, divisors d with 1 < d < k).

%C The total numbers of divisors of the first 31 terms are 2, 2, 2, 2, 2, 3, 2, 2, 4, 2, 2, 2, 2, 2, 4, 4, 4, 4, 4, 2, 8, 2, 2, 8, 2, 4, 2, 8, 4, 2, 2. - _N. J. A. Sloane_, Dec 01 2019

%H Rémy Sigrist and Giovanni Resta, <a href="/A330070/b330070.txt">Table of n, a(n) for n = 1..48</a>

%H Rémy Sigrist, <a href="/A330070/a330070.txt">C++ program for A330070</a>

%e a(6) = 25 = 5 * 5: 5 is not in the sequence, and no combination of 2, 3, 7, 11, and 17 sums to 25.

%o (C++) See Links section.

%Y Cf. A330071, A330126.

%K nonn

%O 1,1

%A _J. Stauduhar_, Nov 30 2019

%E Terms a(24)-a(31) from Christian Lawson-Perfect, Dec 01 2019

%E Terms a(32)-a(37) from _Rémy Sigrist_, Dec 02 2019