A250131 a(n) is the odd part of the digital sum of 3^n divided by the maximal possible power of 3.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 5, 1, 5, 1, 5, 1, 1, 7, 7, 1, 1, 1, 7, 1, 7, 1, 11, 1, 1, 5, 5, 1, 5, 11, 5, 1, 5, 11, 1, 7, 13, 1, 1, 13, 13, 5, 1, 5, 5, 1, 7, 13, 11, 5, 17, 17, 1, 5, 13, 1, 17, 17, 1, 5, 1, 17, 19, 5, 17, 1

Offset

1,14

Comments

Consider the sequence {b(n)}, such that b(1)=2, b(2)=3, and for n>=3, b(n)=a(n-2). We conjecture that, if we apply the Eratosthenes-like sieve to b(n) and remove 1's, then we obtain a sequence of primes. Peter J. C. Moses noted that these primes follow with some perturbation of order. For example, 73 appears before 71. Similarly, 101 and 103 appear before 97.

Links

Table of n, a(n) for n=1..77.

Prog

(PARI) a(n) = my(sd = sumdigits(3^n)); sd/(3^(valuation(sd, 3))*2^(valuation(sd, 2))); \\ Michel Marcus, Dec 12 2014

Crossrefs

Cf. A221858, A225039, A225093, A251964.

Sequence in context: A293235 A066803 A089608 * A100615 A293897 A334988

Adjacent sequences: A250128 A250129 A250130 * A250132 A250133 A250134

Keyword

nonn,base

Author

Vladimir Shevelev, Dec 12 2014

Extensions

More terms from Peter J. C. Moses, Dec 12 2014

Status

approved