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Search: id:A136118
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| 5, 4, 7, 12, 19, 17, 25, 20, 10, 28, 45, 42, 39, 17, 37, 21, 36, 35, 13, 33, 65, 28, 67, 32, 52, 40, 74, 31, 70, 85, 35, 16, 60, 70, 77, 68, 42, 30, 105, 76, 59, 26, 74, 49, 115, 19, 125, 115, 102, 110, 92, 56, 103, 29, 145, 100, 114, 77, 92, 47, 63, 108, 152, 95, 22, 116
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OFFSET
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1,1
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EXAMPLE
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a(1)=5 is the least integer m>0 such that A136117(1)-P(m)
is a pentagonal number,
namely P(7)-P(5)=70-35=35=P(5).
a(2)=4 is the least integer m>0 such that A136117(2)-P(m)
is a pentagonal number,
namely P(8)-P(4)=92-22=70=P(7).
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PROGRAM
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(PARI) A136118vect(n, i=-1)=vector(n, k, until(0, for(j=2, #n=sum2sqr((i+=6)^2+1), n[j]%6==[5, 5]|next; n=n[j]; break(2))); n[1]\6+1) /* This uses sum2sqr(), cf. A133388. Below some simpler but much slower code: */ P(n)=n*(3*n-1)/2 /* a.k.a. A000326 */ /*****newline*****/ isPent(t)=P(sqrtint(t*2\3)+1)==t /*****newline*****/ for(i=1, 299, for(j=1, (i+1)\sqrt(2), isPent(P(i)-P(j))&print1(j", ")|next(2)))
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CROSSREFS
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Cf. A000326, A136112-A136117.
Adjacent sequences: A136115 A136116 A136117 this_sequence A136119 A136120 A136121
Sequence in context: A011285 A111421 A021650 this_sequence A105665 A019129 A019208
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KEYWORD
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nonn
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AUTHOR
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M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Dec 25 2007
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