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 A055456 a(n) = smallest number which is not the sum of exactly 1 or of n earlier terms. 1
 1, 3, 2, 13, 4, 5, 6, 7, 8, 9, 10, 11, 12, 183, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA If n-1>0 has not already appeared in sequence then a(n)=n-1, otherwise a(n)=n^2-n+1 EXAMPLE a(3)=2 because 1 is already in the sequence, 2 has not yet appeared (i.e. is not the sum of 1 earlier term) and because the sum of 3 earlier terms is 3, 5 or 7. a(4)=13 because 1, 2 and 3 have already appeared and the sum of 4 earlier terms could be any integer from 4 through to 12. CROSSREFS Cf. A035334. a(n) is not n-1 iff n-1 is in A024556 or equivalently in A002065. Sequence in context: A236435 A218566 A125135 * A198303 A093922 A075555 Adjacent sequences:  A055453 A055454 A055455 * A055457 A055458 A055459 KEYWORD easy,nonn AUTHOR Henry Bottomley, May 19 2000 STATUS approved

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Last modified August 10 00:24 EDT 2020. Contains 336359 sequences. (Running on oeis4.)