Primes whose base c expansion is also the base b expansion of a prime.
by M. F. Hasler, Jan.2014 - under construction : seq’s in yellow = submitted as draft, green = published
b \c | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | other | (b,c) |
2 | (A000040) | 73, 521, 577,... | 2,5,7,11,31,37... ⊂ A077718 | 5,31,131,151,... | ... | ... | ... | 739,811,6571,... | (10,13): | (13,10): | |
3 | 2,7,11,13,41,... | (A000040) | 2,89,137,149,... | ... | 2,13,43,73,... | 2,7,107,401,... | 2,17,73,521,... | 2,11,19,83,... | (10,17): | (17,10): | |
4 | 2,43,61,67,97... | (A000040) | ...13,41,43,61... | ...7,19,37,79... | ...17,59,71,73... | ...11,19,67,89... | ... | (10,19): | (19,10): | ||
5 | 2,7,11,13,19,... | ... | 2,3,11,29,31,... | (A000040) | ... | ...7,17,23,31... | ...17,19,73,89... | ...11,19,29,31... | (10,31): | A235640 ? | |
6 | 3,5,7,11,17,19... | ... | 2,3,5,13,17,... | 2,3,11,31,71,... | (A000040) | ...5,19,61,89... | ...13,17,29,37... | ...5,19,23,41... | (10,32): | A235641 ? | |
7 | 2, 31, 47, 59,... | ... | 2,3,11,23,29... | ...,5,13,17,23... | 2,3,5,17,47,... | (A000040) | ...5,19,53,89... | ...19,41,59,97... | A235642 ? | ||
8 | ... | 2,7,13,31,37... | 2,3,7,11,19,29... | 2,3,11,13,31... | 2,3,5,11,13,23... | 2,3,5,17,47,... | (A000040) | ...19,41,59,97... | (by RGWv) | ...(10,512): | A235643 ? |
9 | 11,13,19,41,... | 2,5,7,11,17,19... | 2,3,29,41,61,... | 2,3,7,11,17,19... | ...13,17,29;59... | 2,5,7,11,17,19... | ...17,37,53,79... | (A000040) | A235395 | (10,1024): | A235644 ? |
10 | (A000040) | (10,11): | (11,10): |
*since primes < min(b,c) are always in the sequence, some initial terms are omitted above, at the profit of one more larger term.
Useful PARI code:
is(p,b=2,c=3)=vecmax(d=digits(p,c))<b&&isprime(vector(#d,i,b^(#d-i))*d~)&&isprime(p)
r(p,b,c)=sum(i=1,#p=digits(p,c),p[i]*b^(#p-i)) \\ “rebase” from base c to base b
forprime(p=1,999,is(p,b,c)&&print1(p","))
forprime(p=1,999,is(p,b,c)&&print1(r(p,b,c)",")) \\ for c < b