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A279389 3 times Mersenne primes A000668. 1
9, 21, 93, 381, 24573, 393213, 1572861, 6442450941, 6917529027641081853, 1856910058928070412348686333, 486777830487640090174734030864381, 510423550381407695195061911147652317181 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also sum of n-th Mersenne prime and the radical of n-th even perfect number.

The binary representation of a(n) has only two zeros, starting with "10" and ending with "01". The sequence begins: 1001, 10101, 1011101, 101111101, 101111111111101,...

LINKS

Table of n, a(n) for n=1..12.

FORMULA

a(n) = 3*A000668(n) = A000668(n) + A139257(n).

a(n) = phi(M(n)) + sigma(sigma(M(n))) = A000010(A000668(n)) + A000203(A000203(A000668(n))) = A000010(A000668(n)) + A051027(A000668(n)).

CROSSREFS

Cf. A000010, A000203, A000396, A000668, A051027, A147757.

Subsequence of A001748, and of A147758, and of A174055, and possibly of other sequences, see below:

Cf. A060482, A068156, A072087, A136252, A144482, A144856, A249780, A269633.

Sequence in context: A146396 A146681 A269633 * A222809 A230648 A177125

Adjacent sequences:  A279386 A279387 A279388 * A279390 A279391 A279392

KEYWORD

nonn

AUTHOR

Omar E. Pol, Dec 20 2016

STATUS

approved

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Last modified September 30 17:27 EDT 2022. Contains 357106 sequences. (Running on oeis4.)