This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A187204 Numbers n such that the bottom entry in the difference table of the divisors of n is 0. 9
 10, 171, 1947, 2619, 265105, 478834027, 974622397, 11373118351 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that A187202(n) = 0. 11373118351 and 1756410942451 are also in the sequence (not necessarily the next two terms). - Donovan Johnson, Aug 05 2011 For every integer m, does there exist a prime p such that abs(A187202(r * m)) > abs(A187202(q * m)) and sign(A187202(r * m)) = sign(A187202(q * m)), and q >= p is prime and prime r > q? - David A. Corneth, Apr 08 2017 No other terms up to 3*10^9. - Michel Marcus, Apr 09 2017 a(9) > 6*10^10. 138662735650982521 and 168248347462416481 are also terms. - Giovanni Resta, Apr 12 2017 LINKS EXAMPLE 10 has divisors 1, 2, 5, 10. The third difference of these numbers is 0.  This is the only possible number having 2 prime factors of the form p*q. The other terms have factorization 171 = 3^2*19, 1947 = 3*11*59, 2619 = 3^3*97, and 265105 = 5*37*1433. MATHEMATICA t = {}; Do[d = Divisors[n]; If[Differences[d, Length[d]-1] == {0}, AppendTo[t, n]], {n, 10^4}]; t (* T. D. Noe, Aug 01 2011 *) PROG (Haskell) import Data.List (elemIndices) a187204 n = a187204_list !! (n-1) a187204_list = map (+ 1) \$ elemIndices 0 \$ map a187202 [1..] -- Reinhard Zumkeller, Aug 02 2011 (PARI) is(n) = my(d=divisors(n)); !sum(i=1, #d, binomial(#d-1, i-1)*d[i]*(-1)^i) \\ David A. Corneth, Apr 08 2017 CROSSREFS Cf. A027750, A187202, A187203, A193671, A193672. Sequence in context: A034830 A098345 A119043 * A133273 A239763 A112703 Adjacent sequences:  A187201 A187202 A187203 * A187205 A187206 A187207 KEYWORD nonn,more,hard AUTHOR Omar E. Pol, Aug 01 2011 EXTENSIONS Suggested by T. D. Noe in the "history" of A187203. a(6)-a(7) from Donovan Johnson, Aug 03 2011 a(8) from Giovanni Resta, Apr 11 2017 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 21 19:25 EDT 2019. Contains 325199 sequences. (Running on oeis4.)