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

77, 95, 145, 221, 295, 371, 395, 407, 437, 445, 469, 545, 559, 649, 695, 745, 763, 895, 959, 995, 1057, 1133, 1145, 1159, 1195, 1253, 1345, 1351, 1513, 1517, 1679, 1745, 1795, 1841, 1895, 1939, 1945, 2021, 2045, 2095, 2101, 2195, 2245, 2249, 2395, 2429

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

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

Python

from sympy import factorint
def is_A064902(n):
    f = factorint(n)
    return (sum([f[i] for i in f]) == 2) and (max(f) % min(f) == 4)
def first_A064902(n):
    x = 1
    an = []
    while len(an) < n:
        if is_A064902(x):an.append(x)
        n += 2
    return an # John Cerkan, Apr 14 2018

Extensions

Offset changed by John Cerkan, Apr 12 2018