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A376746
Semiprimes whose prime factors are the digit reversal of each other.
1
4, 9, 25, 49, 121, 403, 1207, 2701, 7663, 10201, 17161, 22801, 32761, 35143, 36481, 75007, 97969, 117907, 124609, 127087, 139129, 140209, 146689, 173809, 197209, 247021, 257821, 342127, 382387, 528529, 573049, 619369, 635209, 643063, 692443, 743623, 844561, 863041
OFFSET
1,1
COMMENTS
The squares of all palindromic primes (A002385) are a subsequence and these are the only perfect squares.
LINKS
EXAMPLE
121 is a term because 121 = 11 * 11.
403 is a term because 403 = 13 * 31.
1207 is a term because 1207 = 17 * 71.
2701 is a term because 2701 = 37 * 73.
PROG
(PARI) upto(lim)={my(L=List()); forprime(p=2, sqrtint(lim), my(q=fromdigits(Vecrev(digits(p)))); if(isprime(q) && p*q<=lim, listput(L, p*q))); Set(L)}
CROSSREFS
A083815 is a subsequence.
Sequence in context: A001255 A357754 A133019 * A326708 A028866 A146981
KEYWORD
nonn,base
AUTHOR
Andrew Howroyd, Oct 03 2024
STATUS
approved