1,1

a[15] = 69981018761651281 is first of following chain: {69981018761651281, 69981019944706811, 69981021127762351, 69981022310817901, 69981023493873461, 69981024676929031, 69981025859984611} = {P[k], P[k+1], ..., P[k+6]}, where k = A090101[15] and P[x] = 5x^2+5x+1. See A090562, A090563.

po[x_] := 5*x^2+5*x+1 Do[s=po[n]; s0=po[n]; s1=po[n+1]; s2=po[n+2]; s3=po[n+3]; s4=po[n+4]; s5=po[n+5]; s6=po[n+6]; If[IntegerQ[n/100000], Print[{n}]]; If[PrimeQ[s0]&&PrimeQ[s1]&&PrimeQ[s2]&&PrimeQ[s3]&&PrimeQ[s4]&&PrimeQ[s5] &&PrimeQ[s6], Print[s0]], {n, 1, 120000000}]

Cf. A090562, A090563, A090100, A090101, A056561.

Sequence in context: A099115 A076171 A297057 * A320625 A219013 A243130

Adjacent sequences: A090099 A090100 A090101 * A090103 A090104 A090105

Labos Elemer, Dec 15 2003

approved