A225039 -id:A225039 - cp's OEIS frontend

A225516 Primes corresponding to terms of A225430.

7, 13, 5, 19, 11, 31, 17, 37, 43, 23, 29, 61, 67, 73, 79, 41, 47, 97, 103, 53, 109, 59, 127, 139, 71, 151, 157, 163

Offset: 1

Vladimir Shevelev, May 09 2013

nonn

It is a result of application of Eratosthenes-like sieve to sequence of odd parts of sums of digits of n^2 which begins 1,1,9,7,7,9,13,5,... .

Conjecture: the sequence is a permutation of all primes > 3.

Cf. A221858, A225017, A225039, A225040, A225093, A225430.

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

Original entry on oeis.org

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

Vladimir Shevelev, Dec 12 2014

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.

Cf. A221858, A225039, A225093, A251964.

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

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

cp's OEIS Frontend

A225516 Primes corresponding to terms of A225430.

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

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