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A122798
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A P_5-stuttered arithmetic progression with a(n+1) = a(n) if n is a pentagonal number, a(n+1) = a(n)+4 otherwise.
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7
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1, 1, 5, 9, 13, 13, 17, 21, 25, 29, 33, 37, 37, 41, 45, 49, 53, 57, 61, 65, 69, 73, 73, 77, 81, 85, 89, 93, 97, 101, 105, 109, 113, 117, 121, 121, 125, 129, 133, 137, 141, 145, 149, 153, 157, 161, 165, 169, 173, 177, 181, 181, 185, 189, 193, 197, 201, 205, 209
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OFFSET
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1,3
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COMMENTS
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P_5(i) = the i-th pentagonal number.
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REFERENCES
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G. D. Bullington, The Connell Sum Sequence, J. Integer Seq. 10 (2007), Article 07.2.6. (includes direct formula for a(n))
D. Iannucci and D. Mills-Taylor, On Generalizing the Connell Sequence, Journal of Integer Sequences v.2 (1999) Article 99.1.7.
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LINKS
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Table of n, a(n) for n=1..59.
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FORMULA
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a(n) = A045929(n) - n + 1.
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PROG
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(PARI) isPentag(n) = {if (! issquare(24*n+1, &res), return (0)); if ( (res + 1) % 6, return (0), return (1)); }
lista(m) = {aa = 1; for (i=1, m, print1(aa, ", "); if (! isPentag(i), aa += 4); ); } \\ Michel Marcus, Apr 01 2013
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CROSSREFS
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Cf. A001614, A122793, A122794, A122795, A122796, A122797, A122799, A122800.
Sequence in context: A080781 A079357 A080455 * A189464 A130333 A080579
Adjacent sequences: A122795 A122796 A122797 * A122799 A122800 A122801
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KEYWORD
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nonn,easy
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AUTHOR
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Grady Bullington (bullingt(AT)uwosh.edu), Sep 14 2006
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EXTENSIONS
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Definition corrected by Michel Marcus, Apr 01 2013
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STATUS
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approved
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