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A076886
Smallest palindrome with exactly n prime factors (counted with multiplicity).
5
1, 2, 4, 8, 88, 252, 2772, 27872, 2112, 4224, 8448, 44544, 48384, 2977792, 27011072, 405504, 4091904, 441606144, 405909504, 886898688, 677707776, 4285005824, 276486684672, 21128282112, 633498894336, 2701312131072, 6739855589376, 29142024192, 65892155129856
OFFSET
0,2
COMMENTS
2^n <= A239697(n) <= a(n). - Michael S. Branicky, Oct 02 2020
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50 (terms 0..30 from Michael S. Branicky and terms 31..35 from David A. Corneth)
Andrew Howroyd, PARI Program
EXAMPLE
a(4)=88 because 88 is the smallest palindromic number with 4 prime factors, 2^3*11 (counted with multiplicity).
PROG
(Python)
from sympy import factorint
def A076886(n):
d = 1
while True:
half = (d+1)//2
for left in range(10**(half-1), 10**half):
strleft = str(left)
if d%2 == 0:
m = int(strleft + strleft[::-1])
else:
m = int(strleft + (strleft[:-1])[::-1])
if sum(list(factorint(m).values())) == n:
return m
d += 1
print([A076886(n) for n in range(17)]) # Michael S. Branicky, Oct 02 2020
CROSSREFS
Cf. A239697.
Sequence in context: A348050 A239697 A237913 * A309565 A046385 A068664
KEYWORD
base,nonn
AUTHOR
Shyam Sunder Gupta, Nov 25 2002
EXTENSIONS
Edited and extended by Robert G. Wilson v, Dec 02 2002
a(26) corrected and a(27)-a(28) from Michael S. Branicky, Oct 02 2020
STATUS
approved