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A064904 Semiprimes p1*p2 such that p2 mod p1 = 6, with p2 > p1. 1
91, 187, 247, 287, 391, 581, 667, 671, 679, 913, 923, 973, 1147, 1169, 1261, 1267, 1397, 1561, 1591, 1639, 1757, 1919, 1927, 1937, 2051, 2123, 2149, 2443, 2491, 2641, 2933, 2951, 3031, 3091, 3127, 3227, 3281, 3521, 3817, 3841, 3859, 4087, 4109, 4207 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
Module[{pp=200}, Select[Union[Times@@@Select[Subsets[Prime[Range[pp]], {2}], Mod[#[[2]], #[[1]]]==6&]], #<=7Prime[pp]&]](* Harvey P. Dale, Oct 08 2020 *)
PROG
(Python)
from sympy import factorint
def is_A064904(n):
f = factorint(n)
return (sum([f[i] for i in f]) == 2) and (max(f) % min(f) == 6) # John Cerkan, Apr 14 2018
(PARI) isok(n) = my(f = factor(n)); (#f~ == 2) && (vecmax(f[, 2]) < 2) && ((f[2, 1] % f[1, 1]) == 6); \\ Michel Marcus, Apr 16 2018
CROSSREFS
Cf. A001358 (p2 mod p1 = 0), A064899-A064911.
Sequence in context: A370053 A037998 A063367 * A352133 A044423 A044804
KEYWORD
nonn
AUTHOR
Patrick De Geest, Oct 13 2001
EXTENSIONS
Offset changed by John Cerkan, Apr 12 2018
STATUS
approved

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Last modified April 20 00:26 EDT 2024. Contains 371798 sequences. (Running on oeis4.)