

A036304


Composite numbers whose prime factors contain no digits other than 1 and 4.


2



121, 451, 1331, 1681, 4961, 14641, 18491, 45221, 48851, 54571, 68921, 125521, 158521, 161051, 168551, 182081, 203401, 452551, 455521, 467851, 485221, 497431, 537361, 590851, 600281, 758131, 1380731, 1686781, 1697851, 1743731, 1771561
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OFFSET

1,1


COMMENTS



LINKS



FORMULA

Sum_{n>=1} 1/a(n) = Product_{p in A020452} (p/(p  1))  Sum_{p in A020452} 1/p  1 = 0.0122909749... .  Amiram Eldar, May 18 2022


EXAMPLE

The composite 4961 = 11^2 * 41 is in the sequence as the digits of its prime factors are either 1 or 4.  David A. Corneth, Oct 17 2020


CROSSREFS



KEYWORD

nonn,easy,base


AUTHOR



STATUS

approved



