|
|
A143641
|
|
Odd prime-proof numbers (A118118) not ending in 5.
|
|
4
|
|
|
212159, 595631, 872897, 1203623, 1293671, 1566691, 1702357, 1830661, 3716213, 3964169, 4103917, 4134953, 4173921, 4310617, 4376703, 4586509, 4703801, 4749187, 4801387, 4928909, 5005353, 5051179, 5231739, 5258901, 5317573
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Most "prime-proof" numbers are even or multiples of 5, cf. A118118.
|
|
LINKS
|
|
|
PROG
|
(PARI) forstep( i=1, 10^7, 2, i%5 || next; isA118118(i) && print1(i", "))
(Magma) IsA143641:=function(n); D:=Intseq(n); return Intseq(n)[1] ne 5 and forall{ <k, j>: k in [1..#D], j in [0..9] | not IsPrime(Seqint(Insert(D, k, k, [j]))) }; end function; [ n: n in [1..4000000 by 2] | IsA143641(n) ]; // Klaus Brockhaus, Mar 03 2011
(Python)
from sympy import isprime
from itertools import count, islice
def selfplusneighs(n):
s = str(n); d = "0123456789"; L = len(s)
yield from (int(s[:i]+c+s[i+1:]) for c in d for i in range(L))
def agen():
for n in count(1, 2):
if n%5 == 0: continue
if all(not isprime(k) for k in selfplusneighs(n)):
yield n
|
|
CROSSREFS
|
|
|
KEYWORD
|
base,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|