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A273157 Numbers which have nonpositive entries in the difference table of their divisors (complement of A273130). 1
6, 10, 12, 14, 15, 18, 20, 22, 24, 26, 28, 30, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 50, 52, 54, 56, 58, 60, 62, 63, 66, 68, 70, 72, 74, 75, 76, 77, 78, 80, 82, 84, 86, 88, 90, 91, 92, 94, 96, 98, 99, 100, 102, 104, 105, 106, 108, 110, 112, 114, 116, 117 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Primorial numbers (A002110) greater than 2 are in this sequence.
LINKS
EXAMPLE
30 is in this sequence because the difference table of the divisors of 30 is:
[1, 2, 3, 5, 6, 10, 15, 30]
[1, 1, 2, 1, 4, 5, 15]
[0, 1, -1, 3, 1, 10]
[1, -2, 4, -2, 9]
[-3, 6, -6, 11]
[9, -12, 17]
[-21, 29]
[50]
PROG
(Sage)
def nsf(z):
D = divisors(z)
T = matrix(ZZ, len(D))
for m, d in enumerate(D):
T[0, m] = d
for k in range(m-1, -1, -1) :
T[m-k, k] = T[m-k-1, k+1] - T[m-k-1, k]
if T[m-k, k] <= 0: return True
return False
print([n for n in range(1, 100) if nsf(n)])
CROSSREFS
Cf. A069059, A187202, A273102, A273103, A273109, A273130 (complement).
Sequence in context: A100658 A182301 A069059 * A139587 A201463 A119313
KEYWORD
nonn
AUTHOR
Peter Luschny, May 16 2016
STATUS
approved

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Last modified June 14 23:20 EDT 2024. Contains 373401 sequences. (Running on oeis4.)