A064909 - OEIS

%I #26 May 15 2021 11:47:07

%S 481,1157,1343,1921,2171,2263,2369,2509,3077,3097,3427,3523,3683,4171,

%T 4537,4541,4811,5213,5263,5389,5543,6107,6227,6707,7123,7241,8279,

%U 8593,8621,8717,8857,8873,9353,9607,10411,10537,11359,11461,11567,11747,11761,11819

%N Semiprimes p1*p2 such that p2 > p1 and p2 mod p1 = 11.

%H John Cerkan, <a href="/A064909/b064909.txt">Table of n, a(n) for n = 1..10000</a>

%t pmp11Q[n_]:=Module[{fi=FactorInteger[n][[All,1]]},Mod[fi[[2]],fi[[1]]] == 11]; Select[ Range[12000],PrimeNu[#]==PrimeOmega[#]==2&&pmp11Q[#]&] (* _Harvey P. Dale_, Jun 25 2018 *)

%o (Python)

%o from sympy import factorint

%o def is_A064909(n):

%o     f = factorint(n)

%o     return (sum([f[i] for i in f]) == 2) and (max(f) % min(f) == 11)

%o def first_A064909(n):

%o     x = 1

%o     an = []

%o     while len(an) < n:

%o         if is_A064909(x): an.append(x)

%o         x += 2

%o     return an # _John Cerkan_, Apr 14 2018

%o (PARI) isok(n) = my(f = factor(n)); (#f~ == 2) && (vecmax(f[,2]) < 2) && ((f[2,1] % f[1,1]) == 11);

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

%K nonn

%O 1,1

%A _Patrick De Geest_, Oct 13 2001

%E Offset and name fixed by _John Cerkan_, Apr 12 2018