

A309560


a(1) = a(2) = 1, a(3) = 2, a(4) = 3, a(5) = 5, a(6) = a(7) = 6, a(8) = 7; a(n) = a(na(n1)) + a(na(n2)) + a(na(n3)) + a(na(n4)) for n > 8.


1



1, 1, 2, 3, 5, 6, 6, 7, 8, 9, 11, 11, 10, 12, 13, 16, 15, 14, 16, 17, 20, 19, 17, 20, 23, 22, 23, 23, 24, 25, 26, 27, 27, 27, 29, 30, 31, 32, 30, 33, 35, 34, 34, 37, 38, 37, 36, 42, 38, 40, 42, 41, 45, 41, 43, 47, 48, 48, 49, 43, 45, 53, 52, 58, 44, 48, 54, 58
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OFFSET

1,3


COMMENTS

This sequence is well defined for n = 1..1000000000; however, it is not known if this sequence is defined for all positive n.


LINKS

Rémy Sigrist, Table of n, a(n) for n = 1..10000
Rémy Sigrist, Density plot of the first 10000000 terms
Rémy Sigrist, C++ program to search for this type of sequences
Index entries for Hofstadtertype sequences


EXAMPLE

a(10) = a(10a(9)) + a(10a(8)) + a(10a(7)) + a(10a(6)) = a(108) + a(107) + a(106) + a(106) = a(2) + a(3) + a(4) + a(4) = 1 + 2 + 3 + 3 = 9.


PROG

(PARI) a = vector(68); a[1] = a[2] = 1; a[3] = 2; a[4] = 3; a[5] = 5; a[6] = a[7] = 6; a[8] = 7; for (n=9, #a, a[n] = a[na[n1]] + a[na[n2]] + a[na[n3]] + a[na[n4]]); print (a)
(MAGMA) I:=[1, 1, 2, 3, 5, 6, 6, 7]; [n le 8 select I[n] else Self(nSelf(n1))+Self(nSelf(n2))+Self(nSelf(n3)) + Self(nSelf(n4)): n in [1..70]]; // Marius A. Burtea, Aug 07 2019


CROSSREFS

Cf. A005185, A292351.
Sequence in context: A165089 A165083 A165085 * A128054 A175081 A023834
Adjacent sequences: A309557 A309558 A309559 * A309561 A309562 A309563


KEYWORD

nonn,look


AUTHOR

Altug Alkan and Rémy Sigrist, Aug 07 2019


STATUS

approved



