



1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 16, 17, 18, 19, 21, 23, 24, 25, 27, 29, 30, 31, 32, 36, 37, 41, 43, 47, 48, 49, 53, 54, 59, 61, 63, 64, 65, 67, 70, 71, 72, 73, 79, 81, 83, 89, 96, 97, 101, 103, 107, 108, 109, 113, 121, 125, 127, 128, 131, 133, 137, 139, 144
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OFFSET

1,2


COMMENTS

A number n is present if its prime factorization n = p_a * p_b * p_c * ... * p_i * p_j * p_k^e_k, where a <= b <= c <= ... <= i <= j < k are the indices of prime factors, not necessarily all distinct, except that j < k, and the greatest prime divisor p_k [with k = A061395(n)] may occur multiple times, satisfies the condition that the first differences of those prime indices (a0, ba, cb, ..., ji, kj) form a palindrome.


LINKS

Antti Karttunen, Table of n, a(n) for n = 1..2185


EXAMPLE

4 = p_1^2 is present, as the first differences (deltas) of the prime indices (excluding the extra copies of the largest prime factor 2), form a palindrome: (10) = (1).
18 = 2*3*3 = p_1 * p_2 * p_2 is present, as the deltas of the indices of its nondistinct prime factors, (excluding the extra copies of the largest prime factor 3) form a palindrome: (10, 21) = (1,1).
60 = 2*2*3*5 = p_1 * p_1 * p_2 * p_3 is NOT present, as the deltas of prime indices (10, 11, 21, 32) = (1,0,1,1) do NOT form a palindrome.
Also, any of the cases mentioned in the Example section of A243058 as being present there, are also present in this sequence.


PROG

(Scheme, with Antti Karttunen's IntSeqlibrary)
(define A243068 (FIXEDPOINTS 1 1 A242420))


CROSSREFS

Fixed points of A242420.
Differs from A242413 for the first time at n=36, where a(36)=61, while A242413(36)=60.
A000040 and A243058 are subsequences.
Cf. A242414, A242417.
Sequence in context: A213006 A072303 A242413 * A081061 A317589 A141807
Adjacent sequences: A243065 A243066 A243067 * A243069 A243070 A243071


KEYWORD

nonn


AUTHOR

Antti Karttunen, Jun 01 2014


STATUS

approved



