A064904 Semiprimes p1*p2 such that p2 mod p1 = 6, with p2 > p1.

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

Offset: 1

Author

Patrick De Geest, Oct 13 2001

Keywords

• nonn

Links

• John Cerkan, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358 (p2 mod p1 = 0), A064899-A064911.

Programs

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 *)

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

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

Extensions

Offset changed by John Cerkan, Apr 12 2018