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A376700
The values of i in primes of the form 2^i*3^j - 1 (A005105) in the order of their appearance.
3
0, 2, 1, 3, 2, 1, 3, 5, 4, 1, 3, 2, 7, 6, 7, 4, 3, 5, 2, 7, 5, 1, 11, 8, 13, 2, 1, 6, 5, 10, 8, 13, 17, 6, 11, 15, 4, 14, 3, 11, 19, 18, 12, 1, 7, 17, 13, 21, 4, 9, 2, 18, 17, 21, 7, 15, 3, 31, 8, 24, 13, 23, 12, 1, 28, 22, 19, 27, 27, 13, 34, 22, 11, 13, 10, 20, 1, 18, 23, 38
OFFSET
1,2
LINKS
FORMULA
a(n) = A007814(A005105(n)+1).
MATHEMATICA
With[{lim = 10^12}, IntegerExponent[Select[Sort@ Flatten@Table[2^i*3^j - 1, {i, 0, Log2[lim]}, {j, 0, Log[3, lim/2^i]}], PrimeQ] + 1, 2]]
PROG
(PARI) lista(lim) = {my(s = List()); for(i = 0, logint(lim, 2), for(j = 0, logint(lim >> i, 3), listput(s, 2^i * 3^j - 1))); s = Set(s); for(i = 1, #s, if(isprime(s[i]), print1(valuation(s[i] + 1, 2), ", "))); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Oct 02 2024
STATUS
approved