cp's OEIS Frontend

A064902 Semiprimes p1*p2 such that p2 mod p1 = 4, with p2 > p1.

%I A064902 #22 Apr 16 2018 19:10:45
%S A064902 77,95,145,221,295,371,395,407,437,445,469,545,559,649,695,745,763,
%T A064902 895,959,995,1057,1133,1145,1159,1195,1253,1345,1351,1513,1517,1679,
%U A064902 1745,1795,1841,1895,1939,1945,2021,2045,2095,2101,2195,2245,2249,2395,2429
%N A064902 Semiprimes p1*p2 such that p2 mod p1 = 4, with p2 > p1.
%H A064902 John Cerkan, <a href="/A064902/b064902.txt">Table of n, a(n) for n = 1..10000</a>
%o A064902 (Python)
%o A064902 from sympy import factorint
%o A064902 def is_A064902(n):
%o A064902     f = factorint(n)
%o A064902     return (sum([f[i] for i in f]) == 2) and (max(f) % min(f) == 4)
%o A064902 def first_A064902(n):
%o A064902     x = 1
%o A064902     an = []
%o A064902     while len(an) < n:
%o A064902         if is_A064902(x):an.append(x)
%o A064902         n += 2
%o A064902     return an # _John Cerkan_, Apr 14 2018
%o A064902 (PARI) isok(n) = my(f = factor(n)); (#f~ == 2) && (vecmax(f[,2]) < 2) && ((f[2,1] % f[1,1]) == 4); \\ _Michel Marcus_, Apr 16 2018
%Y A064902 Cf. A001358 (p2 mod p1 = 0), A064899-A064911.
%K A064902 nonn
%O A064902 1,1
%A A064902 _Patrick De Geest_, Oct 13 2001
%E A064902 Offset changed by _John Cerkan_, Apr 12 2018